Bityite is considered a rare

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

, and it is an endmember to the

margarite Margarite is a calcium rich member of the mica group of the phyllosilicates with formula: Ca Al2(Al2 Si2) O10(O H)2. It forms white to pinkish or yellowish gray masses or thin laminae. It crystallizes in the monoclinic crystal system. It typical ...

mica sub-group found within the

phyllosilicate 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, silica (silicon dioxide, ) is usually consid ...

group. The mineral was first described by Antoine François Alfred Lacroix in 1908, and later its chemical composition was concluded by Professor Hugo Strunz.Strunz, H. (1956) Bityit, ein berylliumglimmer. Zeitschrift für Kristallographie, 107, 325-330. Bityite has a close association with

beryl Beryl ( ) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several ...

, and it generally crystallizes in pseudomorphs after it, or in cavities associated with reformed beryl crystals.Lahti, S. I. and Saikkonen, R. (1985) Bityite 2M₁ from Eräjärvi compared with related Li-Be brittle micas. Bulletin of the Geological Society of Finland, 57, 207-215. The mineral is considered a late-stage constituent in

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...

bearing

pegmatites A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic co ...

,Lin, J-C. and Guggenheim, S. (1983) The crystal structure of a Li,Be-rich brittle mica: a dioctaheral-trioctahedral intermediate. American Mineralogist, 68, 130-142. and has only been encountered in a few localities throughout the world. The mineral was named by LacroixLacroix, A. (1908) Les minéraux de felons de pegmatite à tourmaline lithique de Madagascar. Bulletin de la Société de Française et de Minéralogie, 31, 218-247 after Mt. Bity,

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

from where it was first discovered.

Geologic occurrence

The first description of bityite was by Lacroix in 1908. and it was discovered on Mt. Bity,

within a pegmatite named Sahatany fiel

It was later found in a

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...

quarry A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envir ...

from Londonderry, Western Australia

Rowledge, H.P. and Hayton, J.D. (1947) Two new beryllium minerals from Londonderry. Journal and Proceedings of the Royal Society of Western Australia, 33, 45-52. and further occurrences have been found from the Middle Urals

and three pegmatites in Zimbabwe

Gallagher, M.J. and Hawkes, J.R. (1966) Beryllium minerals from Rhodesia and Uganda. Bulletin of the Geological Survey of Great Britain, 25, 59-75. And most recently, occurrences from the Pizzo Marcio, Val Vigezzo area in Piedmont, Italy

have been discovered. The most recent analysis for bityite found in the literature is for a sample from the Maantienvarsi pegmatite dyke in the Eräjärvi area in Orives

southern

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...

. The sample from Maantienvarsi occurs in close association with

; either in cavities with altered beryl crystals, or as a

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...

after beryl. The mineral has been found in cavities with perthic

microcline Microcline (KAlSi3O8) is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slo ...

, albitic

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavag ...

and

tourmaline Tourmaline ( ) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is a gemstone and can be found in a wide variety of colors. The te ...

; the pseudomorphs filled with bityite have been found to contain amounts 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 sca ...

bertrandite Bertrandite is a beryllium sorosilicate hydroxide mineral with composition: Be4Si2O7(OH)2. Bertrandite is a colorless to pale yellow orthorhombic mineral with a hardness of 6-7. It is commonly found in beryllium rich pegmatites and is in part an ...

, fluorapatite,

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

and beryl. The mineral substitutes into portions of beryl crystals, and is either a

hydrothermal alteration Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical co ...

product or a late stage magmatic mineral.

Chemical composition

The current chemical formula for bityite is ''CaLiAl₂(AlBeSi₂)O₁₀(OH)₂.''Anthony, J.W., Bideaux, R., Bladh, K., and Nichols, M. (2003) Bityite CaLiAl₂(AlBeSi₂)O₁₀(OH)₂ Handbook of Mineralogy, Mineral Data Publishing (Republished by the Mineralogical Society of America)
link to bityite
/ref> The mineral was analyzed by Lacroix, and concluded to be a new mineral rich with concentrations of

and

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...

. In 1947, Rowledge and Hayton discovered a new mineral from Londonderry,

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...

with a similar chemical composition; they named it bowleyite. However, mineralogical studies performed by Strunz later confirmed that the chemical composition and properties for bowleyite were actually bityite. A recent chemical analysis found in the literature was performed with heavy liquids on a sample of bityite from the Maantienvarsi dyke to derive a computed formula for bityite based on 24 oxygens; the computed chemical formula is ''Ca_1.19K_0.03Na_0.02(Li_1.19Al_3.68Mg_0.35Fe_0.13)_5.35(Al_1.53Be_2.21Si_4.26)₈O_19.30(OH)_4.54F_0.16''. The samples from Mt. Bity, Maantienvarsi, and Londonderry, Western Australia show similar chemical compositions as compared to the computed composition for bityite; the chemical analysis for the three samples and the computed composition are tabulated in the adjacent table.

Structure

The atomic structure derived by X-Ray powder and optical analysis of bityite is that of a two layer modification that also exhibits a complex affinity to twinning. From studies done on mica flakes from the Maantienvarsi sample, the mineral is a two layer-type modification of

polytype In materials science, polymorphism describes the existence of a solid material in more than one form or crystal structure. Polymorphism is a form of isomerism. Any crystalline material can exhibit the phenomenon. Allotropy refers to polymorphism ...

''2M₁.'' Bityite has a mica structure, shown in adjacent figure, which consists of

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...

and

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...

sheets separated by an interlayer cation. The mineral is considered a brittle mica, and it can be distinguished from the true micas by a layer charge per unit of approximately -2.0; in consequence, their interlayer cation is usually

calcium Calcium is a chemical element with the 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 t ...

or barium.Deer, W.A, Howie, R. A., and Zussman, J. (1963) Rock-Forming Minerals, Volume 3, Sheet Silicates. Wiley, New York. Bityite’s structure consists of a coupled substitution it exhibits between the sheets of polyhedra; the coupled substitution of beryllium for

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

within the tetrahedral sites allows a single lithium substitution for a vacancy without any additional octahedral substitutions. The transfer is completed by creating a tetrahedral sheet composition of Si₂BeAl. The coupled substitution of lithium for vacancy and the beryllium for the tetrahedral aluminium maintains all the charges balanced; thereby, resulting in the trioctahedral end member for the

sub-group of the

group.Guggenheim, S. (1984) The brittle micas. Reviews in Mineralogy, 13, 61-104.

Physical properties

Bityite exhibits a strong pearly luster, and occurs as a fine scaled white yellowish mass which is usually smaller than 0.3mm in diameter; and, its opacity is transparent to translucent. Physical properties analyses conducted with precision photographs using

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

-filtered molybdenum radiation indicates that bityite exhibits

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

symmetry, and is part of the C2/c

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...

. The

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, for example) does not necessaril ...

dimensions are ''a = 4.99 Å,'' ''b = 8.68 Å,'' ''c = 19.04 Å,'' ''β=95.17°'', with a volume of 821.33 Å³. The refraction indices measured by the immersion method are ''α = 1.650'', ''β = 1.658'', ''γ = 1.660'' with 2V calculation of 52.9°. Bityite’s

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

is 3.14, and it has a hardness of 4−4.5 based on Mohs scale of hardness. Bityite’s luster is vitreous and pearly on cleavages, and it has a perfect micaceous cleavage on the

miller index Miller indices form a notation system in crystallography for lattice planes in crystal (Bravais) lattices. In particular, a family of lattice planes of a given (direct) Bravais lattice is determined by three integers ''h'', ''k'', and ''� ...

. Bityite’s crystal habit can display thin and pseudohexagonal platy crystals.

References

{{Phyllosilicates Mica group Monoclinic minerals Minerals in space group 15