Bityite
Encyclopedia
Bityite is considered a rare mineral
, and it is an endmember to the margarite
mica sub-group found within the phyllosilicate group. The mineral was first described by Antoine François Alfred Lacroix in 1908, and later its chemical composition was concluded by Professor Hugo Strunz
. Bityite has a close association with beryl
, and it generally crystallizes in pseudomorphs after it, or in cavities associated with reformed beryl crystals. The mineral is considered a late-stage constituent in lithium
bearing pegmatites, and has only been encountered in a few localities throughout the world. The mineral was named by Lacroix after Mt. Bity, Madagascar
from where it was first discovered.
within a pegmatite
named Sahatany field http://www.mindat.org/loc-57020.html. It was later found in a feldspar
quarry
from Londonderry, Western Australia
http://www.mindat.org/loc-17479.html, and further occurrences have been found from the Middle Urals
http://www.mindat.org/loc-2645.html, and three pegmatites in Zimbabwe
http://www.mindat.org/loc-21891.html. And most recently, occurrences from the Pizzo Marcio, Val Vigezzo area in Piedmont, Italyhttp://www.mindat.org/loc-25849.html 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 Orivesi http://www.mindat.org/loc-16490.html, southern Finland
. The sample from Maantienvarsi occurs in close association with beryl
; either in cavities with altered beryl crystals, or as a pseudomorph
after beryl. The mineral has been found in cavities with perthic
microcline
, albitic
plagioclase
, muscovite
and tourmaline
; the pseudomorphs filled with bityite have been found to contain amounts of fluorite
, bertrandite
, fluorapatite
, quartz
and beryl. The mineral substitutes into portions of beryl crystals, and is either a hydrothermal alteration product or a late stage magmatic mineral.
and beryllium
. In 1947, Rowledge and Hayton discovered a new mineral from Londonderry, Western Australia
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 Ca1.19K0.03Na0.02(Li1.19Al3.68Mg0.35Fe0.13)5.35(Al1.53Be2.21Si4.26)8O19.30(OH)4.54F0.16.
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.
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 2M1. Bityite has a mica structure, shown in adjacent figure, which consists of tetrahedral and octahedral 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
or barium
. Bityite’s structure consists of a coupled substitution
it exhibits between the sheets of polyherdra; the coupled substitution of beryllium for aluminium
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 margarite
sub-group of the phyllosilicate group.
, 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
-filtered molybdenum
radiation
indicates that bityite exhibits monoclinic symmetry, and is part of the C2/c space group
. The unit cell 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
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 {001} miller index
. Bityite’s crystal habit
can display thin and pseudohexagonal platy crystals.
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...
, and it is an endmember to the margarite
Margarite
Margarite is a calcium rich member of the mica group of the phyllosilicates with formula: CaAl2O102. It forms white to pinkish or yellowish gray masses or thin laminae. It crystallizes in the monoclinic crystal system. It typically has a specific gravity of around 3 and a Mohs hardness of 4...
mica sub-group found within the phyllosilicate 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 classification
Nickel–Strunz classification is a scheme for categorizing minerals based upon their chemical composition, introduced by German mineralogist Karl Hugo Strunz in his 1941 Mineralogische Tabellen. The 4th edition was edited by Christel Tennyson too . It was followed by A.S...
. Bityite has a close association with beryl
Beryl
The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al26. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare...
, and it generally crystallizes in pseudomorphs after it, or in cavities associated with reformed beryl crystals. The mineral is considered a late-stage constituent in lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
bearing pegmatites, and has only been encountered in a few localities throughout the world. The mineral was named by Lacroix after Mt. Bity, Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of 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, MadagascarMadagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
within a pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
named Sahatany field http://www.mindat.org/loc-57020.html. It was later found in a feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
quarry
Quarry
A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...
from Londonderry, Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
http://www.mindat.org/loc-17479.html, and further occurrences have been found from the Middle Urals
Ural Mountains
The Ural Mountains , or simply the Urals, are a mountain range that runs approximately from north to south through western Russia, from the coast of the Arctic Ocean to the Ural River and northwestern Kazakhstan. Their eastern side is usually considered the natural boundary between Europe and Asia...
http://www.mindat.org/loc-2645.html, and three pegmatites in Zimbabwe
Zimbabwe
Zimbabwe is a landlocked country located in the southern part of the African continent, between the Zambezi and Limpopo rivers. It is bordered by South Africa to the south, Botswana to the southwest, Zambia and a tip of Namibia to the northwest and Mozambique to the east. Zimbabwe has three...
http://www.mindat.org/loc-21891.html. And most recently, occurrences from the Pizzo Marcio, Val Vigezzo area in Piedmont, Italyhttp://www.mindat.org/loc-25849.html have been discovered. The most recent analysis for bityite found in the literature is for a sample from the Maantienvarsi pegmatite dyke
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
in the Eräjärvi area in Orivesi http://www.mindat.org/loc-16490.html, southern Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
. The sample from Maantienvarsi occurs in close association with beryl
Beryl
The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al26. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare...
; either in cavities with altered beryl crystals, or as a pseudomorph
Pseudomorph
In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form , resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another...
after beryl. The mineral has been found in cavities with perthic
Perthite
Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar . Typically the host grain is orthoclase or microcline, and the lamellae are albite...
microcline
Microcline
Microcline 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 slow cooling of orthoclase; it is more stable at lower temperatures...
, albitic
Albite
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...
plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
, muscovite
Muscovite
Muscovite is a phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a highly-perfect basal cleavage yielding remarkably-thin laminæ which are often highly elastic...
and tourmaline
Tourmaline
Tourmaline is a crystal boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors...
; the pseudomorphs filled with bityite have been found to contain amounts 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...
, bertrandite
Bertrandite
Bertrandite is a beryllium sorosilicate hydroxide mineral with composition: Be4Si2O72. 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 alteration of beryl. Bertrandite often occurs as a...
, fluorapatite
Fluorapatite
Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca53F . Fluorapatite is a hard crystalline solid. Although samples can have various color , the pure mineral is colorless as expected for a material lacking transition metals...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
and beryl. The mineral substitutes into portions of beryl crystals, and is either a hydrothermal alteration product or a late stage magmatic mineral.
Chemical Composition
The current chemical formula for bityite is CaLiAl2(AlBeSi2)O10(OH)2. The mineral was analyzed by Lacroix, and concluded to be a new mineral rich with concentrations of lithiumLithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
and beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
. In 1947, Rowledge and Hayton discovered a new mineral from Londonderry, Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
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 Ca1.19K0.03Na0.02(Li1.19Al3.68Mg0.35Fe0.13)5.35(Al1.53Be2.21Si4.26)8O19.30(OH)4.54F0.16.
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 analysisSpectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
of bityite is that of a two layer modification that also exhibits a complex affinity to 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....
. From studies done on mica
Mica
The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...
flakes from the Maantienvarsi sample, the mineral is a two layer-type modification of polytype 2M1. Bityite has a mica structure, shown in adjacent figure, which consists of tetrahedral and octahedral 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
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...
or barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
. Bityite’s structure consists of a coupled substitution
Substitution reaction
In a substitution reaction, a functional group in a particular chemical compound is replaced by another group. In organic chemistry, the electrophilic and nucleophilic substitution reactions are of prime importance...
it exhibits between the sheets of polyherdra; the coupled substitution of beryllium for 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....
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 margarite
Margarite
Margarite is a calcium rich member of the mica group of the phyllosilicates with formula: CaAl2O102. It forms white to pinkish or yellowish gray masses or thin laminae. It crystallizes in the monoclinic crystal system. It typically has a specific gravity of around 3 and a Mohs hardness of 4...
sub-group of the phyllosilicate group.
Physical Properties
Bityite exhibits a strong pearly 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....
, 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
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
-filtered molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
indicates that bityite exhibits monoclinic symmetry, and is part of the C2/c 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...
. The unit cell dimensions are a = 4.99 Å
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
, b = 8.68 Å, c = 19.04 Å, β=95.17°, with a volume of 821.33 Å3. The refraction indices
Optical mineralogy
Optical mineralogy is the study of minerals and rocks by measuring their optical properties. Most commonly, rock and mineral samples are prepared as thin sections or grain mounts for study in the laboratory with a petrographic microscope...
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
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 3.14, and it has a hardness of 4-4.5 based on Mohs
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...
scale of hardness. Bityite’s luster is vitreous and pearly on cleavages, and it has a perfect micaceous 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...
on the {001} miller index
Miller index
Miller indices form a notation system in crystallography for planes and directions in crystal lattices.In particular, a family of lattice planes is determined by three integers h, k, and ℓ, the Miller indices. They are written , and each index denotes a plane orthogonal to a direction in the...
. Bityite’s crystal habit
Crystal habit
Crystal habit is an overall description of the visible external shape of a mineral. This description can apply to an individual crystal or an assembly of crystals or aggregates....
can display thin and pseudohexagonal platy crystals.