Stilbite
Encyclopedia
Stilbite is the name of a series of tectosilicate
mineral
s 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:
Stilbite-Ca, by far the more common of the two, is a hydrous calcium sodium and aluminium silicate, Na
Ca
4(Si
27Al
9)O
72·28(H
2O
). In the case of stilbite-Na, sodium dominates over calcium. The species are visually indistinguishable, and the series name stilbite is still used whenever testing has not been performed.
and stilbite were considered to be identical minerals. After they were found to be two separate species, in 1818, the name desmine ("a bundle") was proposed for stilbite, and this name is still employed in Germany
. The English name "stilbite" is from the Greek stilbein = to shine, because of the pearly luster of the {010} faces.
, Si, ions and aluminium
, Al, ions occupy equivalent sites, and can substitute for each other, but they have a different charge (Si4+ and Al3+) so the ions occupying the Na/Ca site have to adjust to maintain charge balance. There is a continuous series
between stellerite
, whose formula can be written as Ca4(Si28Al8)O72·28(H2O), and stilbite, and another a continuous series between stilbite and barrerite
, Na8(Si28Al8)O72·26(H2O).
Epistilbite is a distinct zeolite species unrelated to stilbite.
2/m, meaning that it has one twofold axis of rotational symmetry
perpendicular to a mirror plane
. The twofold axis is the crystal axis b, and the a and c crystal axes lie in the mirror plane. For a monoclinic crystal a and c are inclined to each other at an angle β which is not a right angle. For stilbite β is nearly 130°. Stilbite crystals, however, appear to be almost orthorhombic
, and a larger unit cell can be chosen, containing two formula units (Z = 2) such that it looks like an orthorhombic cell, with all three crystal axes very nearly mutually perpendicular. The mineral is said to be pseudo-orthorhombic.
Non-endmember
forms of stilbite may be triclinic
or even truly orthorhombic, indeed the framework can have symmetry ranging from orthorhombic to triclinic in a single crystal.
s are typically thin tabular, flattened parallel to the dominant cleavage
and elongated along the a axis. Aggregates may be sheaf-like or in bow-ties, also fibrous and globular. Twinning
, cruciform and penetration, is extremely common on {001}.
is generally vitreous, and on the perfect cleavage
parallel to the plane of symmetry it is markedly pearly. The streak
is white and crystals are transparent to translucent. The hardness is 3½ to 4 and the specific gravity
2.12 to 2.22. Cleavage is perfect on {010}, poor on {001}. The mineral is brittle, with a conchoidal or uneven fracture
. It is not radioactive.
Stilbite is biaxial (-) with refractive indices
:
The unit cell can be considered as a monoclinic cell with β close to 130° and one formula unit per unit cell (Z = 1), or as a larger pseudo-orthorhombic cell with β close to 90° and Z = 2.
Cell Parameters for the monoclinic cell:
Cell parameters for the pseudo-orthorhombic cell:
The framework of stilbite is pseudo-orthorhombic with the open channels typical of zeolites. It has 10-member rings and 8-member rings forming channels parallel to a and pseudo-orthorhombic c respectively.
hydrothermal mineral. It occurs in the amygdaloidal
cavities of basalt
ic volcanic rocks, in andesites
, gneiss
and hydrothermal veins
. It also forms in hot springs deposits
, and as a cementing agent in some sandstones and conglomerates
. Stilbite has not been found in sedimentary tuff
deposits or deep-sea deposits. Associated minerals are other zeolites, prehnite
, calcite
and quartz
.
, Faroe Islands
, Isle of Skye, Bay of Fundy
, Nova Scotia
, northern New Jersey
and North Carolina
. Salmon-pink crystals occur with pale green apophyllite
in the Deccan Traps
near Mumbai
(Bombay) and Pune
, India
; white sheaf-like groups encrust the calcite (Iceland-spar
) of Berufjord near Djupivogr in Iceland; brown sheafs are found near Paterson, New Jersey
in the United States
; and crystals of a brick-red color are found at Old Kilpatrick, Scotland
.
Iceland is generally considered to be the type locality
for stilbite-Ca. It is presumed to be the Helgusta Iceland Spar Mine, along Reydarfjordur. Excellent white bow ties of stilbite are found here on calcite and quartz, associated with heulandite and laumontite
in cavities.
The type locality for stilbite-Na is Cape Pula, Pula, Cagliari
Province, Sardinia
, Italy
. Small, lustrous, white or pink, pointed blades of stilbite-Na, and formless masses, up to 5 cm in diameter, have been found there, covering a thin crust of reddish heulandite
in large fractures and cavities in the highly weathered volcanic andesite
or rhyolite
.
The Tertiary
Deccan basalts of western India are the most prolific sources of stilbite in the world. Stilbite is the most abundant zeolite in the tholeiitic basalt plateaux near Nasik and Pune and decreases in abundance toward the coast at Mumbai.
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...
s of 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. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association
International Mineralogical Association
The International Mineralogical Association is an international group of 38 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 4000 plus known mineral species...
changed it to a series name, with the mineral species being named:
- stilbite-Ca
- stilbite-Na
Stilbite-Ca, by far the more common of the two, is a hydrous calcium sodium and aluminium silicate, Na
Na
Na or na may refer to:*Na , a Japanese kana*Na or Mesua ferrea, a species of tree native to Sri Lanka*.na, the top-level domain for Namibia*Na people, a small tribal group in India...
Ca
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...
4(Si
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
27Al
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....
9)O
O
O is the fifteenth letter and a vowel in the basic modern Latin alphabet.The letter was derived from the Semitic `Ayin , which represented a consonant, probably , the sound represented by the Arabic letter ع called `Ayn. This Semitic letter in its original form seems to have been inspired by a...
72·28(H
H
H .) is the eighth letter in the basic modern Latin alphabet.-History:The Semitic letter ⟨ח⟩ most likely represented the voiceless pharyngeal fricative . The form of the letter probably stood for a fence or posts....
2O
O
O is the fifteenth letter and a vowel in the basic modern Latin alphabet.The letter was derived from the Semitic `Ayin , which represented a consonant, probably , the sound represented by the Arabic letter ع called `Ayn. This Semitic letter in its original form seems to have been inspired by a...
). In the case of stilbite-Na, sodium dominates over calcium. The species are visually indistinguishable, and the series name stilbite is still used whenever testing has not been performed.
History
At one time heulanditeHeulandite
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:*...
and stilbite were considered to be identical minerals. After they were found to be two separate species, in 1818, the name desmine ("a bundle") was proposed for stilbite, and this name is still employed in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. The English name "stilbite" is from the Greek stilbein = to shine, because of the pearly luster of the {010} faces.
Chemistry and related species
Stilbite shows a wide variation in exchangeable cations (positively charged ions). SiliconSilicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, Si, ions and aluminium
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....
, Al, ions occupy equivalent sites, and can substitute for each other, but they have a different charge (Si4+ and Al3+) so the ions occupying the Na/Ca site have to adjust to maintain charge balance. There is a continuous series
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
between stellerite
Stellerite
Stellerite has a general formula of CaAl2Si7O18]·7H2O. It is named after Georg Wilhelm Steller who was a German explorer and zoologist that discovered it. Like most rare minerals, there aren’t many commercial uses for stellerite yet. Mineral collectors are lucky to find it in good enough crystal...
, whose formula can be written as Ca4(Si28Al8)O72·28(H2O), and stilbite, and another a continuous series between stilbite and barrerite
Barrerite
Barrerite is a tectosilicate mineral and a member of the zeolite family. It is one of the rarer zeolites and found only at Rocky Pass, Kuiu Island, Alaska. It was named for Richard Maling Barrer , a British teacher born in New Zealand....
, Na8(Si28Al8)O72·26(H2O).
Epistilbite is a distinct zeolite species unrelated to stilbite.
Crystal class
Stilbite is usually 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...
2/m, meaning that it has one twofold axis of rotational symmetry
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...
perpendicular to a mirror 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...
. The twofold axis is the crystal axis b, and the a and c crystal axes lie in the mirror plane. For a monoclinic crystal a and c are inclined to each other at an angle β which is not a right angle. For stilbite β is nearly 130°. Stilbite crystals, however, appear to be almost 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 a larger unit cell can be chosen, containing two formula units (Z = 2) such that it looks like an orthorhombic cell, with all three crystal axes very nearly mutually perpendicular. The mineral is said to be pseudo-orthorhombic.
Non-endmember
Endmember (mineralogy)
An endmember in mineralogy is a mineral that is at the extreme end of a mineral series in terms of purity. Minerals often can be described as solid solutions with varying compositions of some chemical elements, rather than as substances with an exact chemical formula...
forms of stilbite may be triclinic
Triclinic crystal system
thumb|180px|Triclinic In crystallography, the triclinic crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system...
or even truly orthorhombic, indeed the framework can have symmetry ranging from orthorhombic to triclinic in a single crystal.
Habit
CrystalCrystal
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...
s are typically thin tabular, flattened parallel to the dominant 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...
and elongated along the a axis. Aggregates may be sheaf-like or in bow-ties, also fibrous and globular. 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....
, cruciform and penetration, is extremely common on {001}.
Physical and optical properties
The color is usually colorless or white, also yellow, brown, pink, salmon, orange, red, green, blue or black. The lusterLustre (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....
is generally vitreous, and on the perfect 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...
parallel to the plane of symmetry it is markedly pearly. The streak
Streak (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...
is white and crystals are transparent to translucent. The hardness is 3½ to 4 and the 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...
2.12 to 2.22. Cleavage is perfect on {010}, poor on {001}. The mineral is brittle, with a conchoidal or uneven 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....
. It is not radioactive.
Stilbite is biaxial (-) 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 = 1.479 to 1.492, Ny = 1.485 to 1.500, Nz = 1.489 to 1.505
- Nx = 1.484 to 1.500, Ny = 1.492 to 1.507, Nz = 1.494 to 1.513
Unit cell and structure
Where sources give cell parameters for stilbite-Na, they are the same as those for stilbite-Ca.The unit cell can be considered as a monoclinic cell with β close to 130° and one formula unit per unit cell (Z = 1), or as a larger pseudo-orthorhombic cell with β close to 90° and Z = 2.
Cell Parameters for the monoclinic cell:
- a = 13.595 to 13.69 Å, b = 18.197 to 18.31 Å, c = 11.265 to 11.30 Å, β = 127.94 to 128.1°
- a = 13.63 Å, b = 18.17 Å, c = 11.31 Å, β = 129.166°
- a = 13.60 to 13.69 Å, b = 18.20 to 18.31 Å, c = 11.27 Å, β = 128°
Cell parameters for the pseudo-orthorhombic cell:
- a = 13.595 to 13.69 Å, b = 18.197 to 18.31 Å, c = 17.775 to 17.86 Å, β = 90.00 to 90.91°
- a = 13.595 to 13.657 Å, b = 18.197 to 18.309 Å, c = 17.775 to 17.842 Å, β = 90:05 to 90.91° (Z is doubled to Z = 4 because the formula unit halved to NaCa2Al5Si13O36.14H2O)
- a=13.69 Å, b=18.25 Å, c=11.31 Å, β =128.2°
- a = 13.60 to 13.69 Å, b = 18.20 to 18.31 Å, c = 17.78 to 17.86 Å, β = 90.0 to 90.91°
The framework of stilbite is pseudo-orthorhombic with the open channels typical of zeolites. It has 10-member rings and 8-member rings forming channels parallel to a and pseudo-orthorhombic c respectively.
Uses
The open channels in the stilbite structure act like a molecular sieve, enabling it to separate hydrocarbons in the process of petroleum refining.Environment
Stilbite is a low-temperature secondarySupergene (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...
hydrothermal mineral. It occurs in the amygdaloidal
Vesicular texture
Vesicular texture is a volcanic rock texture characterised by a rock being pitted with many cavities at its surface and inside. The texture is often found in extrusive aphanitic, or glassy, igneous rock...
cavities of 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...
ic volcanic rocks, in andesites
Andesites
Andesites is an extinct genus of cephalopod belonging to the Ammonite subclass....
, gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
and hydrothermal veins
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...
. It also forms in hot springs deposits
Hot spring
A hot spring is a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal hot springs in many locations all over the crust of the earth.-Definitions:...
, and as a cementing agent in some sandstones and conglomerates
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
. Stilbite has not been found in sedimentary tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
deposits or deep-sea deposits. Associated minerals are other zeolites, 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...
, 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:...
and 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,...
.
Localities
Stilbite is abundant in the volcanic rocks of IcelandIceland
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...
, Faroe Islands
Faroe Islands
The Faroe Islands are an island group situated between the Norwegian Sea and the North Atlantic Ocean, approximately halfway between Scotland and Iceland. The Faroe Islands are a self-governing territory within the Kingdom of Denmark, along with Denmark proper and Greenland...
, Isle of Skye, Bay of Fundy
Bay of Fundy
The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...
, Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
, northern New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
and North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
. Salmon-pink crystals occur with pale green 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...
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 Mumbai
Mumbai
Mumbai , formerly known as Bombay in English, is the capital of the Indian state of Maharashtra. It is the most populous city in India, and the fourth most populous city in the world, with a total metropolitan area population of approximately 20.5 million...
(Bombay) and Pune
Pune District
Pune District is situated in Maharashtra state of India. Pune city is the district headquarters. In the last census on 2001, the total population of the district was 7,232,555, making it the fourth most populous district in India . Urban population comprises 58.08% of the total population...
, 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...
; white sheaf-like groups encrust the calcite (Iceland-spar
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:...
) of Berufjord near Djupivogr in Iceland; brown sheafs are found near Paterson, New Jersey
Paterson, New Jersey
Paterson is a city serving as the county seat of Passaic County, New Jersey, United States. As of the 2010 United States Census, its population was 146,199, rendering it New Jersey's third largest city and one of the largest cities in the New York City Metropolitan Area, despite a decrease of 3,023...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
; and crystals of a brick-red color are found at Old Kilpatrick, 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...
.
Iceland is generally considered to be the 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....
for stilbite-Ca. It is presumed to be the Helgusta Iceland Spar Mine, along Reydarfjordur. Excellent white bow ties of stilbite are found here on calcite and quartz, associated with heulandite and laumontite
Laumontite
Laumontite is a mineral, one of the zeolite group. Its molecular formula is 2·4H2O, a hydrated calcium-aluminium silicate. Potassium or sodium may substitute for the calcium but only in very small amounts....
in cavities.
The type locality for stilbite-Na is Cape Pula, Pula, Cagliari
Cagliari
Cagliari is the capital of the island of Sardinia, a region of Italy. Cagliari's Sardinian name Casteddu literally means castle. It has about 156,000 inhabitants, or about 480,000 including the outlying townships : Elmas, Assemini, Capoterra, Selargius, Sestu, Monserrato, Quartucciu, Quartu...
Province, Sardinia
Sardinia
Sardinia is the second-largest island in the Mediterranean Sea . It is an autonomous region of Italy, and the nearest land masses are the French island of Corsica, the Italian Peninsula, Sicily, Tunisia and the Spanish Balearic Islands.The name Sardinia is from the pre-Roman noun *sard[],...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. Small, lustrous, white or pink, pointed blades of stilbite-Na, and formless masses, up to 5 cm in diameter, have been found there, covering a thin crust of reddish 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:*...
in large fractures and cavities in the highly weathered volcanic andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
or rhyolite
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
.
The Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
Deccan basalts of western India are the most prolific sources of stilbite in the world. Stilbite is the most abundant zeolite in the tholeiitic basalt plateaux near Nasik and Pune and decreases in abundance toward the coast at Mumbai.
External links
- Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=00200