Fluorellestadite
Encyclopedia
Fluorellestadite is a rare nesosilicate
of calcium
, with sulfate
and fluorine
, with the chemical formula Ca10(SiO4)3(SO4)3F2. It is a member of the apatite
group, and forms a series with hydroxylellestadite.
, USA.
In 1982 Rouse and Dunn showed that the Si:S ratio was close to 1:1, giving the formula Ca10(SiO4)3(SO4)3X2, where X represents fluorine
(F), hydroxyl
(OH) or chlorine
(Cl), and they named minerals in this group the ellestadite group. The end members of the group were named hydroxylellestadite (X = OH), fluorellestadite (X = F) and chlorellestadite (X = Cl); ideal end-member chlorellestadite is assumed not to exist in nature, although it has been synthesized. Wilkeite was discredited as a unique species, as it is not an end member of any solid solution
series, but an intermediate member.
The name fluorellestadite was changed to ellestadite-(F) in 2008 and changed back to fluorellestadite in 2010.
, which are minerals with isolated SiO4 tetrahedra
. They are members of the apatite
group, but whereas phosphorus
is one of the chief constituents of apatite, in ellestadite it is almost completely replaced by sulfur
and silicon
, without appreciably altering the structure. The crystal class
is hexagonal
6/m, space group
P63/m. The tetrahedral groups are arranged to create the 63 screw axis
, and the fluorine
atoms are located in channels parallel to this direction. Some sources give unit cell
parameters for one formula unit
per unit cell (Z = 1), but some scientists consider the formula to be half the value accepted by the International Mineralogical Association
(IMA), i.e. Ca5((Si,S)O4))3F, with two formula units per unit cell (Z = 2). Cell parameters for natural, as opposed to synthetic, material are a = 9.41 to 9.53 Å, and c = 6.90 to 6.94 Å. Rouse and Dunn postulated a hypothetical pure end-member with a = 9.543 Å and c = 6.917 Å. Synthetic material has a = 9.53 to 9.561 Å, and c = 6.91 to 6.920 Å.
or hexagonal prismatic
, poorly terminated crystals, and as fine-grained aggregates. Crystals are transparent and aggregates are translucent. Material from Crestmore, California, is light rose-red or yellow in color, and typically occurs in a matrix of blue calcite
. Material from Russia is pale bluish-green or colorless. The streak
is white with a weak bluish tint, and the luster
is sub-resinous on broken surfaces, but very brilliant on prism
faces.
perpendicular to the long crystal axis
. The mineral is very brittle, and breaks with a conchoidal fracture
. Its hardness
is 4½, between that of fluorite
and apatite
, and its specific gravity
is 3.03 to 3.07, similar to that of fluorite. It is easily soluble in dilute hydrochloric
and nitric acid
s and is not radioactive
. When intensely heated, ellestadite (wilkeite) becomes colorless and then assumes a pale bluish green color on cooling.
The mineral is uniaxial (-)
, with refractive indices
nω = 1.638 to 1.655 and nε = 1.632 to 1.650. It is sometimes fluorescent
, white to blue-white or yellow-white in short-wave ultraviolet
light, and medium white-yellow-brown or weak white in long-wave light.
is Coal Mine No. 44, Kopeisk, Chelyabinsk coal basin, Chelyabinsk Oblast
, Southern Urals, Russia, and type material is held at the Fersman Mineralogical Museum
, Academy of Sciences, Moscow, Russia.
Ellestadite is a skarn
mineral. It occurs associated with diopside
, wollastonite
, idocrase, monticellite
, okenite
, vesuvianite
, calcite
and others at Crestmore, Riverside County, California, USA. At Crestmore a contact zone exists between crystalline limestone
and granodiorite
. The area was quarried for limestone in the early 1900s, revealing varied associations of metamorphic minerals
, including ellestadite (named as wilkeite) with garnet
, vesuvianite
and diopside
, in blue calcite
. At the type locality it was formed in burned fragments of petrified wood
in coal dumps, associated with lime, periclase
, magnesioferrite
, hematite
, srebrodolskite and anhydrite
. Ellestadite (wilkeite) is often altered to okenite
.
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...
of 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...
, with sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
and fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
, with the chemical formula Ca10(SiO4)3(SO4)3F2. It is a member of the apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
group, and forms a series with hydroxylellestadite.
Etymology
The mineral was originally named wilkeite by Eakle and Rogers in 1914, in honour of R. M. Wilke, a mineral collector and dealer. In 1922, a sample of “wilkeite” was analysed and found to be sufficiently different from the material reported by Eakle and Rogers to consider it a new species. The name “ellestadite” was proposed, in honour of Reuben B Ellestad (1900–1993), an American analytic chemist from the Laboratory for Rock Analysis, University of MinnesotaUniversity of Minnesota
The University of Minnesota, Twin Cities is a public research university located in Minneapolis and St. Paul, Minnesota, United States. It is the oldest and largest part of the University of Minnesota system and has the fourth-largest main campus student body in the United States, with 52,557...
, USA.
In 1982 Rouse and Dunn showed that the Si:S ratio was close to 1:1, giving the formula Ca10(SiO4)3(SO4)3X2, where X represents fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
(F), hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
(OH) or chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
(Cl), and they named minerals in this group the ellestadite group. The end members of the group were named hydroxylellestadite (X = OH), fluorellestadite (X = F) and chlorellestadite (X = Cl); ideal end-member chlorellestadite is assumed not to exist in nature, although it has been synthesized. Wilkeite was discredited as a unique species, as it is not an end member of any solid solution
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...
series, but an intermediate member.
The name fluorellestadite was changed to ellestadite-(F) in 2008 and changed back to fluorellestadite in 2010.
Structure
The ellestadites are nesosilicatesSilicate 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...
, which are minerals with isolated SiO4 tetrahedra
Tetrahedron
In geometry, a tetrahedron is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids...
. They are members of the apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
group, but whereas phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
is one of the chief constituents of apatite, in ellestadite it is almost completely replaced by sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and silicon
Silicon
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...
, without appreciably altering the structure. The crystal class
Crystallographic point group
In crystallography, a crystallographic point group is a set of symmetry operations, like rotations or reflections, that leave a central point fixed while moving other directions and faces of the crystal to the positions of features of the same kind...
is hexagonal
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
6/m, 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...
P63/m. The tetrahedral groups are arranged to create the 63 screw axis
Screw axis
The screw axis of an object is a line that is simultaneously the axis of rotation and the line along which a translation occurs...
, and the fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
atoms are located in channels parallel to this direction. Some sources give unit cell
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...
parameters for one formula unit
Formula unit
A formula unit in chemistry is the empirical formula of an ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound...
per unit cell (Z = 1), but some scientists consider the formula to be half the value accepted 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...
(IMA), i.e. Ca5((Si,S)O4))3F, with two formula units per unit cell (Z = 2). Cell parameters for natural, as opposed to synthetic, material are a = 9.41 to 9.53 Å, and c = 6.90 to 6.94 Å. Rouse and Dunn postulated a hypothetical pure end-member with a = 9.543 Å and c = 6.917 Å. Synthetic material has a = 9.53 to 9.561 Å, and c = 6.91 to 6.920 Å.
Appearance
Fluorellestadite occurs as acicularAcicular (crystal habit)
Acicular, in mineralogy, refers to a crystal habit composed of a radiating mass of slender, needle-like crystals. Minerals with this habit tend to be fragile and complete, undamaged specimens can be uncommon.-Examples:...
or hexagonal prismatic
Prism (geometry)
In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...
, poorly terminated crystals, and as fine-grained aggregates. Crystals are transparent and aggregates are translucent. Material from Crestmore, California, is light rose-red or yellow in color, and typically occurs in a matrix of blue 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:...
. Material from Russia is pale bluish-green or colorless. 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 with a weak bluish tint, and the 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....
is sub-resinous on broken surfaces, but very brilliant on prism
Prism
-Science and mathematics:* Prism , a transparent object which refracts light** Dispersive prism, the most familiar type of optical prism* Prism , a kind of polyhedron* Prism , a type of sedimentary deposit-Books, comics and magazines:...
faces.
Physical properties
Fluorellestadite shows imperfect cleavageCleavage (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...
perpendicular to the long 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...
. The mineral is very brittle, and breaks with a conchoidal 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....
. Its hardness
Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...
is 4½, between that of fluorite
Fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
and apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
, and its 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...
is 3.03 to 3.07, similar to that of fluorite. It is easily soluble in dilute hydrochloric
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
and nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
s and is 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...
. When intensely heated, ellestadite (wilkeite) becomes colorless and then assumes a pale bluish green color on cooling.
The mineral is uniaxial (-)
Birefringence
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....
nω = 1.638 to 1.655 and nε = 1.632 to 1.650. It is 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...
, white to blue-white or yellow-white in short-wave 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, and medium white-yellow-brown or weak white in long-wave light.
Occurrence and associations
The type localityType 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....
is Coal Mine No. 44, Kopeisk, Chelyabinsk coal basin, Chelyabinsk Oblast
Chelyabinsk Oblast
-External links:*...
, Southern Urals, Russia, and type material is held at the Fersman Mineralogical Museum
Fersman Mineralogical Museum
Fersman Mineralogical Museum is one of the largest mineral museums of the world. Its collections include more than 135,000 items. Among them natural crystals, geodes, druzes and other kinds of mineral treasures. The museum was named after Alexander Fersman....
, Academy of Sciences, Moscow, Russia.
Ellestadite is a skarn
Skarn
Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Archean age limestones in Sweden's Persberg mining district. In modern usage the term "skarn" has been expanded to refer...
mineral. It occurs associated with diopside
Diopside
Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class...
, wollastonite
Wollastonite
Wollastonite is a calcium inosilicate mineral that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or dolostone is subjected to high temperature and pressure sometimes in the presence of silica-bearing fluids...
, idocrase, monticellite
Monticellite
Monticellite and kirschsteinite are gray silicate minerals of the olivine group with compositions CaMgSiO4 and CaFeSiO4, respectively. Most monticellites have the pure magnesium end-member composition but rare ferroan monticellites and magnesio-kirschsteinite are found with between 30 and 75 mol.%...
, okenite
Okenite
Okenite is a silicate mineral that is usually associated with zeolites. It most commonly is found as small white "cotton ball" formations within basalt geodes. These formations are clusters of straight, radiating, fibrous crystals that are both bendable and fragile...
, vesuvianite
Vesuvianite
Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism...
, 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 others at Crestmore, Riverside County, California, USA. At Crestmore a contact zone exists between crystalline limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
and granodiorite
Granodiorite
Granodiorite is an intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. Officially, it is defined as a phaneritic igneous rock with greater than 20% quartz by volume where at least 65% of the feldspar is plagioclase. It usually contains abundant...
. The area was quarried for limestone in the early 1900s, revealing varied associations of metamorphic minerals
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
, including ellestadite (named as wilkeite) with garnet
Garnet
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
, vesuvianite
Vesuvianite
Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism...
and diopside
Diopside
Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class...
, in blue 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:...
. At the type locality it was formed in burned fragments of petrified wood
Petrified wood
Petrified wood is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree having turned completely into stone by the process of permineralization...
in coal dumps, associated with lime, periclase
Periclase
Periclase occurs naturally in contact metamorphic rocks and is a major component of most basic refractory bricks. It is a cubic form of magnesium oxide ....
, magnesioferrite
Magnesioferrite
Magnesioferrite is a magnesium iron oxide mineral, a member of the magnetite series of spinels.Magnesioferrite crystallizes as black metallic octahedral crystals.It is named after its chemical composition of magnesium and ferric iron....
, hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
, srebrodolskite and anhydrite
Anhydrite
Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...
. Ellestadite (wilkeite) is often altered to okenite
Okenite
Okenite is a silicate mineral that is usually associated with zeolites. It most commonly is found as small white "cotton ball" formations within basalt geodes. These formations are clusters of straight, radiating, fibrous crystals that are both bendable and fragile...
.