Scolecite
Encyclopedia
Scolecite is a tectosilicate
mineral
belonging to the zeolite
group; it is a hydrated calcium
silicate
, CaAl
2Si3O
10.3H2O. Only minor amounts of sodium
and traces of potassium
substitute for calcium. There is an absence of barium
, strontium
, iron
and magnesium
. Scolecite is isostructural (having the same structure) with the sodium-calcium zeolite mesolite
and the sodium
zeolite natrolite
, but it does not form a continuous chemical series with either of them. It was described in 1813, and named from the Greek
word, σκώληξ = 'worm' because of its reaction to the blowpipe
flame
.
m with space group
Cc, but crystals are pseudotetragonal
.
Scolecite, like natrolite and mesolite, usually occurs as acicular (needle-like) and fibrous aggregations. It has nearly the same angles between the crystal faces as does natrolite, but natrolite is orthorhombic
and scolecite is monoclinic. The etched figures (figures that arise from the action of a solvent on a crystal face, and indicate its true symmetry) and the pyroelectric
character of scolecite show that it crystal
lizes with a plane
of symmetry, but no axis
of symmetry, that is to say it belongs to the hemihedral
class of the monoclinic system. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicol prism
s. Twinning
on the ortho-pinacoid is usually evident.
framework is the same for scolecite, natrolite and mesolite. Scolecite has long ordered chains, rotated 24° round the axis of the chain. One Ca cation and three H2O molecules are in four ion
sites in the channels parallel to the c crystal axis
. There is no sign of aluminium ions occupying silicon ion sites.
Crystals, however, are pseudotetragonal, and this can be represented by taking a different unit cell, with twice as many formula units (Z = 8) and two long sides and one short one. The axes are redefined, a and b are very nearly equal and the angle β between the new a and c axes is very nearly equal to 90° (a truly tetragonal crystal would have a = b and β = 90° exactly). The sources give the following values:
or pseudo-tetragonal
, and may be square in cross section. It also occurs as radiating groups and fibrous masses. Epitaxial intergrowths (intergrowths of two different crystalline substances in an non-random way) with mesolite
, Na2Ca2Al6Si9O30.8H2O, are common. (Natrolite
, Na2Al2Si3O10.2H2O, does not directly form epitaxial overgrowths on scolecite). All three minerals may be developed in the same crystal.
Scolecite crystals appear to be monoclinic by X-ray analysis
. Common forms include {111},
Scolecite is a tectosilicate
mineral
belonging to the zeolite
group; it is a hydrated calcium
silicate
, CaAl
2Si3O
10.3H2O. Only minor amounts of sodium
and traces of potassium
substitute for calcium. There is an absence of barium
, strontium
, iron
and magnesium
. Scolecite is isostructural (having the same structure) with the sodium-calcium zeolite mesolite
and the sodium
zeolite natrolite
, but it does not form a continuous chemical series with either of them. It was described in 1813, and named from the Greek
word, σκώληξ = 'worm' because of its reaction to the blowpipe
flame
.
m with space group
Cc, but crystals are pseudotetragonal
.
Scolecite, like natrolite and mesolite, usually occurs as acicular (needle-like) and fibrous aggregations. It has nearly the same angles between the crystal faces as does natrolite, but natrolite is orthorhombic
and scolecite is monoclinic. The etched figures (figures that arise from the action of a solvent on a crystal face, and indicate its true symmetry) and the pyroelectric
character of scolecite show that it crystal
lizes with a plane
of symmetry, but no axis
of symmetry, that is to say it belongs to the hemihedral
class of the monoclinic system. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicol prism
s. Twinning
on the ortho-pinacoid is usually evident.
framework is the same for scolecite, natrolite and mesolite. Scolecite has long ordered chains, rotated 24° round the axis of the chain. One Ca cation and three H2O molecules are in four ion
sites in the channels parallel to the c crystal axis
. There is no sign of aluminium ions occupying silicon ion sites.
Crystals, however, are pseudotetragonal, and this can be represented by taking a different unit cell, with twice as many formula units (Z = 8) and two long sides and one short one. The axes are redefined, a and b are very nearly equal and the angle β between the new a and c axes is very nearly equal to 90° (a truly tetragonal crystal would have a = b and β = 90° exactly). The sources give the following values:
or pseudo-tetragonal
, and may be square in cross section. It also occurs as radiating groups and fibrous masses. Epitaxial intergrowths (intergrowths of two different crystalline substances in an non-random way) with mesolite
, Na2Ca2Al6Si9O30.8H2O, are common. (Natrolite
, Na2Al2Si3O10.2H2O, does not directly form epitaxial overgrowths on scolecite). All three minerals may be developed in the same crystal.
Scolecite crystals appear to be monoclinic by X-ray analysis
. Common forms include {111},
Scolecite is a tectosilicate
mineral
belonging to the zeolite
group; it is a hydrated calcium
silicate
, CaAl
2Si3O
10.3H2O. Only minor amounts of sodium
and traces of potassium
substitute for calcium. There is an absence of barium
, strontium
, iron
and magnesium
. Scolecite is isostructural (having the same structure) with the sodium-calcium zeolite mesolite
and the sodium
zeolite natrolite
, but it does not form a continuous chemical series with either of them. It was described in 1813, and named from the Greek
word, σκώληξ = 'worm' because of its reaction to the blowpipe
flame
.
m with space group
Cc, but crystals are pseudotetragonal
.
Scolecite, like natrolite and mesolite, usually occurs as acicular (needle-like) and fibrous aggregations. It has nearly the same angles between the crystal faces as does natrolite, but natrolite is orthorhombic
and scolecite is monoclinic. The etched figures (figures that arise from the action of a solvent on a crystal face, and indicate its true symmetry) and the pyroelectric
character of scolecite show that it crystal
lizes with a plane
of symmetry, but no axis
of symmetry, that is to say it belongs to the hemihedral
class of the monoclinic system. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicol prism
s. Twinning
on the ortho-pinacoid is usually evident.
framework is the same for scolecite, natrolite and mesolite. Scolecite has long ordered chains, rotated 24° round the axis of the chain. One Ca cation and three H2O molecules are in four ion
sites in the channels parallel to the c crystal axis
. There is no sign of aluminium ions occupying silicon ion sites.
Crystals, however, are pseudotetragonal, and this can be represented by taking a different unit cell, with twice as many formula units (Z = 8) and two long sides and one short one. The axes are redefined, a and b are very nearly equal and the angle β between the new a and c axes is very nearly equal to 90° (a truly tetragonal crystal would have a = b and β = 90° exactly). The sources give the following values:
or pseudo-tetragonal
, and may be square in cross section. It also occurs as radiating groups and fibrous masses. Epitaxial intergrowths (intergrowths of two different crystalline substances in an non-random way) with mesolite
, Na2Ca2Al6Si9O30.8H2O, are common. (Natrolite
, Na2Al2Si3O10.2H2O, does not directly form epitaxial overgrowths on scolecite). All three minerals may be developed in the same crystal.
Scolecite crystals appear to be monoclinic by X-ray analysis
. Common forms include {111}, 11}, {101}, {110} and {010}.
and a luster
which is vitreous, or silky for fibrous specimens. It has a Mohs hardness of 5 to 5½ and a specific gravity
in the range 2.16 to 2.40. (2.24 to 2.31 2.25 to 2.29 2.16 to 2.4 2.25 to 2.31. Cleavage
is perfect in two directions parallel to the length of the crystals; the mineral is brittle
with an irregular fracture
. Twinning
is common on {100}, twin axis [001], as penetration
or contact
twins producing V-shaped or fishtail terminations. Scolecite is pyroelectric
and piezoelectric
, sometimes fluorescent
yellow to brown in longwave and shortwave ultraviolet
light. It is soluble in common acids
. Not radioactive
.
(-) with refractive indices
:
Nx = 1.507 to 1.513, Ny = 1.516 to 1.520, Nz = 1.517 to 1.521. Pleochroism
has been reported, X: colorless Y: colorless Z: colorless
. It is a mineral of secondary
origin, and occurs with other zeolites in the amygdaloidal cavities (cavities filled with secondary minerals) of weathered basalts, also in gneisses and amphibolite
s, and in laccolith
s and dikes
derived from syenitic
and gabbro
ic magmas, and in contact metamorphic
zones. It is a hydrothermal
mineral derived from low temperature alteration of basalts and related rocks, associated with other zeolites, calcite
, quartz
and prehnite
. It can be found on top of the calcium zeolites heulandite
, stilbite
and epistilbite.
Associated minerals include quartz
, apophyllite
, babingtonite
, heulandite
, stilbite
and other zeolites.
in Baden-Württemberg
in 1813. Divergent groups of prismatic crystals are found in the basalt
of Berufjördur near Djupivogr, Suður-Múlasýsla
, Iceland
and in the Deccan Traps
near Pune
in India
; hence the synonym poonahlite for this species. Other occurrences include Riverside County, California
; Skye, Scotland
and Santa Catarina, Brazil.
There is no type locality
. Most of the world's finest scolecite specimens are found in the Tertiary Deccan Basalt near Nasik, Pune, in the state of Maharashtra, India.
The quarries in the Nasik region produce large, colourless sprays of well terminated coarse scolecite crystals that are commonly twinned on {100} to form V-shaped terminations with V-shaped striations on {010}. The scolecite is commonly found alone or on stilbite and is covered with laumontite or colourless, pale green or white fluorapophyllite. It is also found in the region as massive radiating material with powellite, and in cavities in basalt as colourless, flattened crystals in radiating sprays on blocky green apophyllite covered by tiny, thin, colourless apophyllite plates.
Scolecite has been reported from many other localities, including Antarctica, Australia, Austria, Brazil, Bulgaria, Canada, Chile, Czechoslovakia, Ethiopia, Faroe Islands, France, Germany, Greenland, Hungary, Iceland, Italy, Japan, Mexico, Mozambique, Nicaragua, Peru, Poland, South Africa, Sweden, Switzerland, Taiwan, United Kingdom, United States and Yugoslavia.
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
belonging to the zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
group; it is a hydrated calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
, CaAl
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
2Si3O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
10.3H2O. Only minor amounts of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and traces of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
substitute for calcium. There is an absence of barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
, strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
. Scolecite is isostructural (having the same structure) with the sodium-calcium zeolite mesolite
Mesolite
Mesolite is a tectosilicate mineral with formula Na2Ca23·8H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance....
and the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
zeolite natrolite
Natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany....
, but it does not form a continuous chemical series with either of them. It was described in 1813, and named from the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
word, σκώληξ = 'worm' because of its reaction to the blowpipe
Blowpipe (tool)
The term blowpipe refers to one of several tools used to direct streams of gases into any of several working media.- Blowpipes for torches :...
flame
Flame
A flame is the visible , gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone...
.
Crystal Class
It is monoclinicMonoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
m with space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
Cc, but crystals are pseudotetragonal
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
.
Scolecite, like natrolite and mesolite, usually occurs as acicular (needle-like) and fibrous aggregations. It has nearly the same angles between the crystal faces as does natrolite, but natrolite is orthorhombic
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
and scolecite is monoclinic. The etched figures (figures that arise from the action of a solvent on a crystal face, and indicate its true symmetry) and the pyroelectric
Pyroelectricity
Pyroelectricity is the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change...
character of scolecite show that it crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
lizes with a plane
Reflection symmetry
Reflection symmetry, reflectional symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection. That is, a figure which does not change upon undergoing a reflection has reflectional symmetry.In 2D there is a line of symmetry, in 3D a...
of symmetry, but no axis
Rotational symmetry
Generally speaking, an object with rotational symmetry is an object that looks the same after a certain amount of rotation. An object may have more than one rotational symmetry; for instance, if reflections or turning it over are not counted, the triskelion appearing on the Isle of Man's flag has...
of symmetry, that is to say it belongs to the hemihedral
Monoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
class of the monoclinic system. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicol prism
Nicol prism
A Nicol prism is a type of polarizer, an optical device used to produce a polarized beam of light from an unpolarized beam. See polarized light. It was the first type of polarizing prism to be invented, in 1828 by William Nicol of Edinburgh...
s. Twinning
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
on the ortho-pinacoid is usually evident.
Structure
The structure of the aluminosilicateAluminosilicate
Aluminosilicate minerals are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals....
framework is the same for scolecite, natrolite and mesolite. Scolecite has long ordered chains, rotated 24° round the axis of the chain. One Ca cation and three H2O molecules are in four ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
sites in the channels parallel to the c crystal axis
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
. There is no sign of aluminium ions occupying silicon ion sites.
Unit Cell
Scolecite is a monoclinic mineral, with the angle β equal to about 109° and four formula units per unit cell (Z = 4). Described in this way, various sources give the following values for the parameters of the unit cell, which has one long side and two short ones:- a = 6.516 to 6.517 Å, b = 18.948 to 18.956 Å, c = 9.761 to 9.765 Å, β = 108.86 to 108.98°
- a = 6.52 to 6.53 Å, b = 18.96 to 18.97 Å, c = 9.76 to 9.78 Å, β = 108.9°
- a = 6.516 Å, b = 18.948 Å, c = 9.761 Å, β = 108.98°
Crystals, however, are pseudotetragonal, and this can be represented by taking a different unit cell, with twice as many formula units (Z = 8) and two long sides and one short one. The axes are redefined, a and b are very nearly equal and the angle β between the new a and c axes is very nearly equal to 90° (a truly tetragonal crystal would have a = b and β = 90° exactly). The sources give the following values:
- a=18.488 to 18.508 Å, b=18.891 to 18.96 Å, c=6.527 to 6.548 Å, β = 90.64 to 90.75°
- a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å β = 90.64°
- a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å, β = 90:64(1)°
- a = 18.51 Å, b = 18.97 Å, c = 6.53 Å, β = 90.6°
Crystal Habits
Scolecite commonly occurs as sprays of thin, prismatic needles, frequently flattened on one side, with slanted terminations and striated parallel to the length of the needles. The crystals appear to be pseudo-orthorhombicOrthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
or pseudo-tetragonal
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
, and may be square in cross section. It also occurs as radiating groups and fibrous masses. Epitaxial intergrowths (intergrowths of two different crystalline substances in an non-random way) with mesolite
Mesolite
Mesolite is a tectosilicate mineral with formula Na2Ca23·8H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance....
, Na2Ca2Al6Si9O30.8H2O, are common. (Natrolite
Natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany....
, Na2Al2Si3O10.2H2O, does not directly form epitaxial overgrowths on scolecite). All three minerals may be developed in the same crystal.
Scolecite crystals appear to be monoclinic by X-ray analysis
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
. Common forms include {111},
Scolecite is a tectosilicate
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
belonging to the zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
group; it is a hydrated calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
, CaAl
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
2Si3O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
10.3H2O. Only minor amounts of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and traces of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
substitute for calcium. There is an absence of barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
, strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
. Scolecite is isostructural (having the same structure) with the sodium-calcium zeolite mesolite
Mesolite
Mesolite is a tectosilicate mineral with formula Na2Ca23·8H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance....
and the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
zeolite natrolite
Natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany....
, but it does not form a continuous chemical series with either of them. It was described in 1813, and named from the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
word, σκώληξ = 'worm' because of its reaction to the blowpipe
Blowpipe (tool)
The term blowpipe refers to one of several tools used to direct streams of gases into any of several working media.- Blowpipes for torches :...
flame
Flame
A flame is the visible , gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone...
.
Crystal Class
It is monoclinicMonoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
m with space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
Cc, but crystals are pseudotetragonal
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
.
Scolecite, like natrolite and mesolite, usually occurs as acicular (needle-like) and fibrous aggregations. It has nearly the same angles between the crystal faces as does natrolite, but natrolite is orthorhombic
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
and scolecite is monoclinic. The etched figures (figures that arise from the action of a solvent on a crystal face, and indicate its true symmetry) and the pyroelectric
Pyroelectricity
Pyroelectricity is the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change...
character of scolecite show that it crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
lizes with a plane
Reflection symmetry
Reflection symmetry, reflectional symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection. That is, a figure which does not change upon undergoing a reflection has reflectional symmetry.In 2D there is a line of symmetry, in 3D a...
of symmetry, but no axis
Rotational symmetry
Generally speaking, an object with rotational symmetry is an object that looks the same after a certain amount of rotation. An object may have more than one rotational symmetry; for instance, if reflections or turning it over are not counted, the triskelion appearing on the Isle of Man's flag has...
of symmetry, that is to say it belongs to the hemihedral
Monoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
class of the monoclinic system. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicol prism
Nicol prism
A Nicol prism is a type of polarizer, an optical device used to produce a polarized beam of light from an unpolarized beam. See polarized light. It was the first type of polarizing prism to be invented, in 1828 by William Nicol of Edinburgh...
s. Twinning
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
on the ortho-pinacoid is usually evident.
Structure
The structure of the aluminosilicateAluminosilicate
Aluminosilicate minerals are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals....
framework is the same for scolecite, natrolite and mesolite. Scolecite has long ordered chains, rotated 24° round the axis of the chain. One Ca cation and three H2O molecules are in four ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
sites in the channels parallel to the c crystal axis
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
. There is no sign of aluminium ions occupying silicon ion sites.
Unit Cell
Scolecite is a monoclinic mineral, with the angle β equal to about 109° and four formula units per unit cell (Z = 4). Described in this way, various sources give the following values for the parameters of the unit cell, which has one long side and two short ones:- a = 6.516 to 6.517 Å, b = 18.948 to 18.956 Å, c = 9.761 to 9.765 Å, β = 108.86 to 108.98°
- a = 6.52 to 6.53 Å, b = 18.96 to 18.97 Å, c = 9.76 to 9.78 Å, β = 108.9°
- a = 6.516 Å, b = 18.948 Å, c = 9.761 Å, β = 108.98°
Crystals, however, are pseudotetragonal, and this can be represented by taking a different unit cell, with twice as many formula units (Z = 8) and two long sides and one short one. The axes are redefined, a and b are very nearly equal and the angle β between the new a and c axes is very nearly equal to 90° (a truly tetragonal crystal would have a = b and β = 90° exactly). The sources give the following values:
- a=18.488 to 18.508 Å, b=18.891 to 18.96 Å, c=6.527 to 6.548 Å, β = 90.64 to 90.75°
- a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å β = 90.64°
- a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å, β = 90:64(1)°
- a = 18.51 Å, b = 18.97 Å, c = 6.53 Å, β = 90.6°
Crystal Habits
Scolecite commonly occurs as sprays of thin, prismatic needles, frequently flattened on one side, with slanted terminations and striated parallel to the length of the needles. The crystals appear to be pseudo-orthorhombicOrthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
or pseudo-tetragonal
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
, and may be square in cross section. It also occurs as radiating groups and fibrous masses. Epitaxial intergrowths (intergrowths of two different crystalline substances in an non-random way) with mesolite
Mesolite
Mesolite is a tectosilicate mineral with formula Na2Ca23·8H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance....
, Na2Ca2Al6Si9O30.8H2O, are common. (Natrolite
Natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany....
, Na2Al2Si3O10.2H2O, does not directly form epitaxial overgrowths on scolecite). All three minerals may be developed in the same crystal.
Scolecite crystals appear to be monoclinic by X-ray analysis
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
. Common forms include {111},
Scolecite is a tectosilicate
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
belonging to the zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
group; it is a hydrated calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
, CaAl
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
2Si3O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
10.3H2O. Only minor amounts of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and traces of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
substitute for calcium. There is an absence of barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
, strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
. Scolecite is isostructural (having the same structure) with the sodium-calcium zeolite mesolite
Mesolite
Mesolite is a tectosilicate mineral with formula Na2Ca23·8H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance....
and the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
zeolite natrolite
Natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany....
, but it does not form a continuous chemical series with either of them. It was described in 1813, and named from the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
word, σκώληξ = 'worm' because of its reaction to the blowpipe
Blowpipe (tool)
The term blowpipe refers to one of several tools used to direct streams of gases into any of several working media.- Blowpipes for torches :...
flame
Flame
A flame is the visible , gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone...
.
Crystal Class
It is monoclinicMonoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
m with space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
Cc, but crystals are pseudotetragonal
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
.
Scolecite, like natrolite and mesolite, usually occurs as acicular (needle-like) and fibrous aggregations. It has nearly the same angles between the crystal faces as does natrolite, but natrolite is orthorhombic
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
and scolecite is monoclinic. The etched figures (figures that arise from the action of a solvent on a crystal face, and indicate its true symmetry) and the pyroelectric
Pyroelectricity
Pyroelectricity is the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change...
character of scolecite show that it crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
lizes with a plane
Reflection symmetry
Reflection symmetry, reflectional symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection. That is, a figure which does not change upon undergoing a reflection has reflectional symmetry.In 2D there is a line of symmetry, in 3D a...
of symmetry, but no axis
Rotational symmetry
Generally speaking, an object with rotational symmetry is an object that looks the same after a certain amount of rotation. An object may have more than one rotational symmetry; for instance, if reflections or turning it over are not counted, the triskelion appearing on the Isle of Man's flag has...
of symmetry, that is to say it belongs to the hemihedral
Monoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
class of the monoclinic system. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicol prism
Nicol prism
A Nicol prism is a type of polarizer, an optical device used to produce a polarized beam of light from an unpolarized beam. See polarized light. It was the first type of polarizing prism to be invented, in 1828 by William Nicol of Edinburgh...
s. Twinning
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
on the ortho-pinacoid is usually evident.
Structure
The structure of the aluminosilicateAluminosilicate
Aluminosilicate minerals are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals....
framework is the same for scolecite, natrolite and mesolite. Scolecite has long ordered chains, rotated 24° round the axis of the chain. One Ca cation and three H2O molecules are in four ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
sites in the channels parallel to the c crystal axis
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
. There is no sign of aluminium ions occupying silicon ion sites.
Unit Cell
Scolecite is a monoclinic mineral, with the angle β equal to about 109° and four formula units per unit cell (Z = 4). Described in this way, various sources give the following values for the parameters of the unit cell, which has one long side and two short ones:- a = 6.516 to 6.517 Å, b = 18.948 to 18.956 Å, c = 9.761 to 9.765 Å, β = 108.86 to 108.98°
- a = 6.52 to 6.53 Å, b = 18.96 to 18.97 Å, c = 9.76 to 9.78 Å, β = 108.9°
- a = 6.516 Å, b = 18.948 Å, c = 9.761 Å, β = 108.98°
Crystals, however, are pseudotetragonal, and this can be represented by taking a different unit cell, with twice as many formula units (Z = 8) and two long sides and one short one. The axes are redefined, a and b are very nearly equal and the angle β between the new a and c axes is very nearly equal to 90° (a truly tetragonal crystal would have a = b and β = 90° exactly). The sources give the following values:
- a=18.488 to 18.508 Å, b=18.891 to 18.96 Å, c=6.527 to 6.548 Å, β = 90.64 to 90.75°
- a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å β = 90.64°
- a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å, β = 90:64(1)°
- a = 18.51 Å, b = 18.97 Å, c = 6.53 Å, β = 90.6°
Crystal Habits
Scolecite commonly occurs as sprays of thin, prismatic needles, frequently flattened on one side, with slanted terminations and striated parallel to the length of the needles. The crystals appear to be pseudo-orthorhombicOrthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
or pseudo-tetragonal
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
, and may be square in cross section. It also occurs as radiating groups and fibrous masses. Epitaxial intergrowths (intergrowths of two different crystalline substances in an non-random way) with mesolite
Mesolite
Mesolite is a tectosilicate mineral with formula Na2Ca23·8H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance....
, Na2Ca2Al6Si9O30.8H2O, are common. (Natrolite
Natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany....
, Na2Al2Si3O10.2H2O, does not directly form epitaxial overgrowths on scolecite). All three minerals may be developed in the same crystal.
Scolecite crystals appear to be monoclinic by X-ray analysis
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
. Common forms include {111}, 11}, {101}, {110} and {010}.
Physical Properties
Scolecite is usually colorless or white, but can also be pink, salmon, red or green. It is transparent to translucent, with a white streakStreak (mineralogy)
The streak of a mineral is the color of the powder produced when it is dragged across an unweathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus...
and a luster
Lustre (mineralogy)
Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance....
which is vitreous, or silky for fibrous specimens. It has a Mohs hardness of 5 to 5½ and a specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
in the range 2.16 to 2.40. (2.24 to 2.31 2.25 to 2.29 2.16 to 2.4 2.25 to 2.31. Cleavage
Cleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...
is perfect in two directions parallel to the length of the crystals; the mineral is brittle
Brittle
A material is brittle if, when subjected to stress, it breaks without significant deformation . Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses ...
with an irregular fracture
Fracture (mineralogy)
In the field of mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a mineral is fractured. Minerals often have a highly distinctive fracture, making it a principal feature used in their identification....
. Twinning
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
is common on {100}, twin axis [001], as penetration
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
or contact
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
twins producing V-shaped or fishtail terminations. Scolecite is pyroelectric
Pyroelectricity
Pyroelectricity is the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change...
and piezoelectric
Piezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
, sometimes fluorescent
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
yellow to brown in longwave and shortwave ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light. It is soluble in common acids
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
. Not radioactive
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
.
Optical Properties
BiaxialBirefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
(-) with refractive indices
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
:
Nx = 1.507 to 1.513, Ny = 1.516 to 1.520, Nz = 1.517 to 1.521. Pleochroism
Pleochroism
Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...
has been reported, X: colorless Y: colorless Z: colorless
Environment
Scolecite is a common zeoliteZeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
. It is a mineral of secondary
Supergene (geology)
In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary sulfide ore minerals and...
origin, and occurs with other zeolites in the amygdaloidal cavities (cavities filled with secondary minerals) of weathered basalts, also in gneisses and amphibolite
Amphibolite
Amphibolite is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are...
s, and in laccolith
Laccolith
A laccolith is a sheet intrusion that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base.Laccoliths tend to form at relatively...
s and dikes
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
derived from syenitic
Syenite
Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or...
and gabbro
Gabbro
Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....
ic magmas, and in contact metamorphic
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
zones. It is a hydrothermal
Vein (geology)
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...
mineral derived from low temperature alteration of basalts and related rocks, associated with other zeolites, calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
and prehnite
Prehnite
Prehnite is a phyllosilicate of calcium and aluminium with the formula: Ca2Al2. Limited Fe3+ substitutes for aluminium in the structure. Prehnite crystallizes in the orthorhombic crystal system, and most oftens forms as stalactitic or botryoidal aggregates, with only just the crests of small...
. It can be found on top of the calcium zeolites heulandite
Heulandite
Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named:*...
, stilbite
Stilbite
Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named:*...
and epistilbite.
Associated minerals include quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, apophyllite
Apophyllite
The name apophyllite refers to a specific group of phyllosilicates, a class of minerals that also includes the micas. Originally, the group name referred to a specific mineral, but was redefined in 1978 to stand for a class of minerals of similar chemical makeup that comprise a solid solution...
, babingtonite
Babingtonite
Babingtonite is a calcium iron manganese inosilicate mineral with the formula Ca2FeSi5O14. It is unusual in that iron completely replaces the aluminium so typical of silicate minerals. It is a very dark green to black translucent mineral crystallizing in the triclinic system with typically radial...
, heulandite
Heulandite
Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named:*...
, stilbite
Stilbite
Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named:*...
and other zeolites.
Localities
Scolecite was first described from KaiserstuhlKaiserstuhl
The „Kaiserstuhl“ is a relatively low mountain range – a Mittelgebirge – with a maximal height of 556.6 m above sea level. It is of volcanic origin and located in the South West of Baden-Württemberg, Germany in the districts of Emmendingen and Breisgau-Hochschwarzwald...
in Baden-Württemberg
Baden-Württemberg
Baden-Württemberg is one of the 16 states of Germany. Baden-Württemberg is in the southwestern part of the country to the east of the Upper Rhine, and is the third largest in both area and population of Germany's sixteen states, with an area of and 10.7 million inhabitants...
in 1813. Divergent groups of prismatic crystals are found in the basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
of Berufjördur near Djupivogr, Suður-Múlasýsla
Suður-Múlasýsla
Suður-Múlasýsla is a county in eastern Iceland. It includes Gerpir, the easternmost point in Iceland....
, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
and in the Deccan Traps
Deccan Traps
The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India and one of the largest volcanic features on Earth. They consist of multiple layers of solidified flood basalt that together are more than thick and cover an area of and a volume of...
near Pune
Pune
Pune , is the eighth largest metropolis in India, the second largest in the state of Maharashtra after Mumbai, and the largest city in the Western Ghats. Once the centre of power of the Maratha Empire, it is situated 560 metres above sea level on the Deccan plateau at the confluence of the Mula ...
in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
; hence the synonym poonahlite for this species. Other occurrences include Riverside County, California
Riverside County, California
Riverside County is a county in the U.S. state of California. One of 58 California counties, it covers in the southern part of the state, and stretches from Orange County to the Colorado River, which forms the state border with Arizona. The county derives its name from the city of Riverside,...
; Skye, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
and Santa Catarina, Brazil.
There is no type locality
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
. Most of the world's finest scolecite specimens are found in the Tertiary Deccan Basalt near Nasik, Pune, in the state of Maharashtra, India.
The quarries in the Nasik region produce large, colourless sprays of well terminated coarse scolecite crystals that are commonly twinned on {100} to form V-shaped terminations with V-shaped striations on {010}. The scolecite is commonly found alone or on stilbite and is covered with laumontite or colourless, pale green or white fluorapophyllite. It is also found in the region as massive radiating material with powellite, and in cavities in basalt as colourless, flattened crystals in radiating sprays on blocky green apophyllite covered by tiny, thin, colourless apophyllite plates.
Scolecite has been reported from many other localities, including Antarctica, Australia, Austria, Brazil, Bulgaria, Canada, Chile, Czechoslovakia, Ethiopia, Faroe Islands, France, Germany, Greenland, Hungary, Iceland, Italy, Japan, Mexico, Mozambique, Nicaragua, Peru, Poland, South Africa, Sweden, Switzerland, Taiwan, United Kingdom, United States and Yugoslavia.
External links
- Mineral galleries
- Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=06889