Fluorellestadite is a rare
nesosilicate
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, the crystalline forms of silica (silicon dio ...
of
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
, with
sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
and
fluorine
Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...
, with the chemical formula Ca
10(SiO
4)
3(SO
4)
3F
2.
[ It is a member of the ]apatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...
group, and forms a series with hydroxylellestadite.
Etymology
The mineral was originally named wilkeite by Eakle and Rogers in 1914, in honor 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.][Duncan McConnell (1937]
The substitution of SiO4 – and SO4 – groups for PO4 -groups in the apatite structure; ellestadite, the end member
American Mineralogist 22: 977–986 The name “ellestadite” was proposed, in honor of Reuben B Ellestad (1900–1993), an American analytic chemist from the Laboratory for Rock Analysis, University of Minnesota
The University of Minnesota Twin Cities (historically known as University of Minnesota) is a public university, public Land-grant university, land-grant research university in the Minneapolis–Saint Paul, Twin Cities of Minneapolis and Saint ...
, US.[
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 is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...
(F), hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
(OH) or chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
(Cl), and they named minerals in this group the ellestadite group.[Roland C. Rouse and Pete J. Dunn (1982]
A contribution to the crystal chemistry of ellestadite and the silicate sulfate apatites
American Mineraleralogist 67: 90–96 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
An endmember (also end-member or end member) in mineralogy is a mineral that is at the extreme end of a mineral series in terms of purity of its chemical composition. Minerals often can be described as solid solutions with varying compositions of ...
of any solid solution
A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...
series, but an intermediate member.[
The name fluorellestadite was changed to ellestadite-(F) in 2008][Burke (2008) The Mineralogical Record 39: 131] and changed back to fluorellestadite in 2010.
Structure
The ellestadites are nesosilicates
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, the crystalline forms of silica (silicon dio ...
, which are minerals with isolated SiO4 tetrahedra
In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...
. They are members of the apatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...
group, but whereas phosphorus
Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
is one of the chief constituents of apatite, in ellestadite it is almost completely replaced by sulfur
Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
and silicon
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
, without appreciably altering the structure.[ The ]crystal class
In crystallography, a crystallographic point group is a three-dimensional point group whose symmetry operations are compatible with a three-dimensional crystallographic lattice. According to the crystallographic restriction it may only contain on ...
is hexagonal
In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°.
Regular hexagon
A regular hexagon is d ...
6/m, space group
In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...
P63/m. The tetrahedral groups are arranged to create the 63 screw axis
A screw axis (helical axis or twist axis) is a line that is simultaneously the axis of rotation and the line along which translation of a body occurs. Chasles' theorem shows that each Euclidean displacement in three-dimensional space has a screw ...
, and the fluorine
Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...
atoms are located in channels parallel to this direction.[ Some sources give ]unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector
In mathematics, a unit vector i ...
parameters for one formula unit
In chemistry, a formula unit is the smallest unit of a non-molecular substance, such as an ionic compound, covalent network solid, or metal. It can also refer to the chemical formula for that unit. Those structures do not consist of discrete mol ...
per unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector
In mathematics, a unit vector i ...
(Z = 1), but some scientists consider the formula to be half the value accepted by the International Mineralogical Association
Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 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 acicular or hexagonal prismatic
An optical prism is a transparent optics, optical element with flat, polished surfaces that are designed to refraction, refract light. At least one surface must be angled—elements with two parallel surfaces are ''not'' prisms. The most fami ...
, poorly terminated crystals, and as fine-grained aggregates.[John J. Jambor and Jacek Puziewicz (1989]
New Mineral Names
American Mineralogist 74: 500, abstract of Chesnokov, Bazhenova and Bushmakin (1987) Zapiski Vses. Mineralog, Obshch 116:743 (in Russian)
[ 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 is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
. 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.][
]
Physical properties
Fluorellestadite shows imperfect cleavage
Cleavage may refer to:
Science
* Cleavage (crystal), the way in which a crystal or mineral tends to split
* Cleavage (embryo), the division of cells in an early embryo
* Cleavage (geology), foliation of rock perpendicular to stress, a result of ...
perpendicular to the long crystal axis
In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat a ...
.[ The mineral is very brittle, and breaks with a conchoidal ]fracture
Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...
.[ Its ]hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...
is , between that of fluorite
Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.
The Mohs scal ...
and apatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...
, and its specific gravity
Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...
is 3.03 to 3.07, similar to that of fluorite. It is easily soluble in dilute hydrochloric
Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastr ...
and nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
s[ and is not ]radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...
.[ When intensely heated, ellestadite (wilkeite) becomes colorless and then assumes a pale bluish green color on cooling.][
The mineral is uniaxial (-), with ]refractive indices
In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
nω = 1.638 to 1.655 and nε = 1.632 to 1.650.[ It is sometimes ]fluorescent
Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with color ...
, white to blue-white or yellow-white in short-wave ultraviolet
Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
light, and medium white-yellow-brown or weak white in long-wave light.[
]
Occurrence and associations
The type locality is Coal Mine No. 44, Kopeisk, Chelyabinsk coal basin, Chelyabinsk Oblast
Chelyabinsk Oblast; , is a federal subjects of Russia, federal subject (an oblast) of Russia in the Ural Mountains region, on the border of Europe and Asia. Its administrative center is the types of inhabited localities in Russia, city of Chel ...
, Southern Urals, Russia,[ and ]type material
In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...
is held at the Fersman Mineralogical Museum
Fersman Mineralogical Museum () is one of the largest mineral museums of the world, located in Moscow, Russia. Its collections include more than 135,000 items. Among them natural crystals, geodes, druses and other kinds of mineral treasures. Th ...
, Academy of Sciences, Moscow, Russia.[
Ellestadite is a ]skarn
Skarns or tactites are coarse-grained metamorphic rocks that form by replacement of carbonate-bearing rocks during regional or contact metamorphism and metasomatism. Skarns may form by metamorphic recrystallization of impure carbonate protoliths, ...
mineral. It occurs associated with diopside
Diopside is a monoclinic pyroxene mineral with composition . 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 ...
, wollastonite
Wollastonite is a calcium Silicate minerals, inosilicate mineral (calcium, Casilicon, Sioxygen, O3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or D ...
, idocrase
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. It was first discovered within ...
, monticellite
Monticellite and kirschsteinite (commonly also spelled kirschteiniteKlein and Hurlbut ''Manual of Mineralogy'' 20th ed., p. 373) are gray silicate minerals of the olivine group with compositions Ca Mg Si O4 and Ca FeSiO4, respectively. Most mont ...
, okenite
Okenite (CaSi2O5·2H2O) 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 crystal ...
, 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. It was first discovered withi ...
, calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
and others at Crestmore, Riverside County
Riverside County is a county located in the southern portion of the U.S. state of California. As of the 2020 census, its population was 2,418,185, making it the fourth-most populous county in California and the 10th-most populous in the Unit ...
, California, US.[ At Crestmore a contact zone exists between crystalline ]limestone
Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
and granodiorite
Granodiorite ( ) is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar.
The term banatite is sometimes used informally for various rocks ranging from gra ...
. The area was quarried for limestone in the early 1900s, revealing varied associations of metamorphic minerals, including ellestadite (named as wilkeite) with garnet
Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.
Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, de ...
, 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. It was first discovered withi ...
and diopside
Diopside is a monoclinic pyroxene mineral with composition . 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 ...
, in blue calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
.[ At the type locality it was formed in burned fragments of ]petrified wood
Petrified wood (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of ''fossilized wood'', the fossilized remains of terrestrial plant, terrestrial vegetation. ''Petrifaction ...
in coal dumps, associated with lime
Lime most commonly refers to:
* Lime (fruit), a green citrus fruit
* Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide
* Lime (color), a color between yellow and green
Lime may also refer to:
Bo ...
, periclase
Periclase is a magnesium mineral that occurs naturally in contact metamorphic rocks and is a major component of most basic refractory bricks. It is a cubic form of magnesium oxide ( Mg O). In nature it usually forms a solid solution with wüstit ...
, 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.
The densit ...
, hematite
Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
, srebrodolskite and anhydrite
Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula 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 ...
.[ Ellestadite (wilkeite) is often altered to ]okenite
Okenite (CaSi2O5·2H2O) 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 crystal ...
.[
]
References
External links
JMol
{{Commons category, position=left
Calcium minerals
Nesosilicates
Crestmore Heights, California
Hexagonal minerals
Minerals in space group 176