Bursaite
Encyclopedia
Bursaite is a sulfosalt
of the lillianite family. It has the formula Pb5Bi4S11 and orthorhombic structure. Bursaite is named after Bursa Province
, Turkey
, where it was discovered. It is generally located in regions rich in sulfur
and commonly occurs alongside other sulfosalts. Its areas of formation are usually those that were once volcanogenic because it is generally aggregated with other mineral
s under intense heating. It was officially delisted as a mineral in 2006, being cited as an intergrowth of two other sulfosalts.
s and granites amidst the Uludag
massif in Bursa, Western Turkey, by scientist Rasit Tolun in 1955. Tolun was also the first to study the chemical composition of bursaite via flotation and superpanner tests. It was originally tested as an aggregate of a larger sulfosalt specimen
. The flotation test involved sodium
-based reagents and oils. The specimen was also chemically analyzed via X-ray spectroscopy
and contained 4.24% pyrite
, 4.78% blende, 5.48% bismuth
and 85.3% Pb5Bi4S11. From these results, bursaite's composition was deduced as 45% Pb, 1% Ag, 38.5% Bi and 14.7% S.
Bursaite is named after the Bursa Province
of Turkey
where it was discovered. After much discussion of bursaite's credibility as a mineral, it was eventually delisted as part of a mass discreditation of minerals.
Bbmm. It was once believed to be monoclinic due to its high reflective power and its oblique extinction.
The mineral contains ionic bonding between its lead
and sulfur
sites. Given the mineral's plate-like habit
, it is likely bonded in sheets. It has the unit cell parameters of a = 13.399(20), b = 20.505(10), c = 4.117(5) and Z = [2]. These numbers yield an axial ratio a:b:c = 0.3078:1:1.5331. The mineral displays strong pleochroism
and weak anisotropy.
. It is composed of many prismatic crystals, which generally form along the [100] axis, intertwined with long, plate-like grains. The prismatic crystals can grow up to 4 mm in length, and can contain polycrystalline aggregates. Twinning
is common in the crystal, usually in (001) planes.
Although bursaite's color
is usually gray, its weak pleochroism can give it a whitish-blue tinge, and its strong anisotropy yields colors ranging from blue to yellow. Many hand samples of bursaite appear to be nearly identical to the mineral lillianite.
In a microscope, bursauite shows distinct high reflective power and oblique extinction. The reflectance values are Rγ' = ~43 and Rα' = ~38 (in nm). The birefringence
is generally weak in air, but stronger when bursaite is immersed in oils.
Bursaite has a hardness of 2.5 on the Mohs scale. It has a gray, metallic luster that appears white in polished sections. The mineral is also known to have good tabular cleavage
along the (100) planes.
, around a metamorphic scheelite deposit near Bursa. It is also associated with the sulfide
veinlets around the Shumilovsk deposit in Russia
, the volcanogenic massive Cofer deposit in Virginia
, and the American Southwest. It also occurs Czech Republic
, Lipari Islands, Mexico
and Sweden
.
Bursaite commonly occurs alongside other sulfosalts, such as sphalerite
, pyrite, chalcopyrite, bismuth and scheelite
. It is usually formed in areas that were once volcanogenic, because of the general nature of sulfosalts and because bursaite is generally aggregated with other minerals under intense heat.
noted that bursaite's X-ray
data shows many coincidences between those of the minerals kobellite and cosalite. However, later studies showed that bursaite's characteristics are nearly identical to the mineral lillianite's.
Bursaite's X-ray diffraction pattern is nearly identical to that of lillianite's, with only slightly more peaks than lillianite. This was eventually explained as a mixture
of two orthorhombic phases
in the mineral. The two phases in bursaite unlike those in lillianite are two Bbmm phases that appear to be exsolution products of phase III, which is simply the synthetic analogue of lillianite. Given this information, it was inferred that bursaite is an intergrowth of two sulfosalt phases, derived from lillianite.
Sulfosalt minerals
Sulfosalt minerals are those complex sulfide minerals with the general formula: AmBnSp; where A represents a metal such as copper, lead, silver, iron and rarely mercury, zinc, vanadium; B usually represents semi-metal such as arsenic, antimony, bismuth and rarely germanium, or metals like tin and...
of the lillianite family. It has the formula Pb5Bi4S11 and orthorhombic structure. Bursaite is named after Bursa Province
Bursa Province
Bursa Province is a province in western Turkey, along the Sea of Marmara. Its adjacent provinces are Balıkesir to the west, Kütahya to the south, Bilecik and Sakarya to the east, Kocaeli to the northeast and Yalova to the north. The province has an area of 11,043 km2 and a population of 3,187,000...
, Turkey
Turkey
Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...
, where it was discovered. It is generally located in regions rich in 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 commonly occurs alongside other sulfosalts. Its areas of formation are usually those that were once volcanogenic because it is generally aggregated with other 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 under intense heating. It was officially delisted as a mineral in 2006, being cited as an intergrowth of two other sulfosalts.
History
Bursaite was discovered in a contact zone between a set of marbleMarble
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite.Geologists use the term "marble" to refer to metamorphosed limestone; however stonemasons use the term more broadly to encompass unmetamorphosed limestone.Marble is commonly used for...
s and granites amidst the Uludag
Uludag
Uludağ , the ancient Mysian Olympus, is a mountain in Bursa Province, Turkey, with an altitude of . It is a popular center for winter sports such as skiing, and a national park of rich flora and fauna...
massif in Bursa, Western Turkey, by scientist Rasit Tolun in 1955. Tolun was also the first to study the chemical composition of bursaite via flotation and superpanner tests. It was originally tested as an aggregate of a larger sulfosalt specimen
Specimen
A specimen is a portion/quantity of material for use in testing, examination, or study.BiologyA laboratory specimen is an individual animal, part of an animal, a plant, part of a plant, or a microorganism, used as a representative to study the properties of the whole population of that species or...
. The flotation test involved sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
-based reagents and oils. The specimen was also chemically analyzed via X-ray spectroscopy
X-ray spectroscopy
X-ray spectroscopy is a gathering name for several spectroscopic techniques for characterization of materials by using x-ray excitation.-Characteristic X-ray Spectroscopy:...
and contained 4.24% pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
, 4.78% blende, 5.48% bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
and 85.3% Pb5Bi4S11. From these results, bursaite's composition was deduced as 45% Pb, 1% Ag, 38.5% Bi and 14.7% S.
Bursaite is named after the Bursa Province
Bursa Province
Bursa Province is a province in western Turkey, along the Sea of Marmara. Its adjacent provinces are Balıkesir to the west, Kütahya to the south, Bilecik and Sakarya to the east, Kocaeli to the northeast and Yalova to the north. The province has an area of 11,043 km2 and a population of 3,187,000...
of Turkey
Turkey
Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...
where it was discovered. After much discussion of bursaite's credibility as a mineral, it was eventually delisted as part of a mass discreditation of minerals.
Structure
Bursaite's structure has not been well studied, and only basic structural information is known. Bursaite is an orthorhombic, dipyramidal mineral. Its symmetry is 2/m2/m2/m, space groupSpace 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...
Bbmm. It was once believed to be monoclinic due to its high reflective power and its oblique extinction.
The mineral contains ionic bonding between its lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
and 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...
sites. Given the mineral's plate-like 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....
, it is likely bonded in sheets. It has the unit cell parameters of a = 13.399(20), b = 20.505(10), c = 4.117(5) and Z = [2]. These numbers yield an axial ratio a:b:c = 0.3078:1:1.5331. The mineral displays strong pleochroism
Pleochroism
Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...
and weak anisotropy.
Physical properties
Bursaite has a tabular, plate-like habitCrystal 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....
. It is composed of many prismatic crystals, which generally form along the [100] axis, intertwined with long, plate-like grains. The prismatic crystals can grow up to 4 mm in length, and can contain polycrystalline aggregates. 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....
is common in the crystal, usually in (001) planes.
Although bursaite's color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
is usually gray, its weak pleochroism can give it a whitish-blue tinge, and its strong anisotropy yields colors ranging from blue to yellow. Many hand samples of bursaite appear to be nearly identical to the mineral lillianite.
In a microscope, bursauite shows distinct high reflective power and oblique extinction. The reflectance values are Rγ' = ~43 and Rα' = ~38 (in nm). The birefringence
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...
is generally weak in air, but stronger when bursaite is immersed in oils.
Bursaite has a hardness of 2.5 on the Mohs scale. It has a gray, metallic luster that appears white in polished sections. The mineral is also known to have good tabular 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...
along the (100) planes.
Occurrence
Like many sulfosalts, bursaite occurs in regions abundant in sulfur. Close to its discovery grounds, it commonly occurs in Uludag, TurkeyUludag
Uludağ , the ancient Mysian Olympus, is a mountain in Bursa Province, Turkey, with an altitude of . It is a popular center for winter sports such as skiing, and a national park of rich flora and fauna...
, around a metamorphic scheelite deposit near Bursa. It is also associated with the sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
veinlets around the Shumilovsk deposit in Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, the volcanogenic massive Cofer deposit in Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
, and the American Southwest. It also occurs Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
, Lipari Islands, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
and Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
.
Bursaite commonly occurs alongside other sulfosalts, such as sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
, pyrite, chalcopyrite, bismuth and scheelite
Scheelite
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws...
. It is usually formed in areas that were once volcanogenic, because of the general nature of sulfosalts and because bursaite is generally aggregated with other minerals under intense heat.
Delisting
Bursaite was official delisted as a mineral as part of a mass discreditation of minerals. It was officially cited as an intergrowth of two sulfosalt phases. Bursaite's status as a mineral was questioned almost from the time of its discovery. In 1956, Michael Fleischer of the American MineralogistAmerican Mineralogist
American Mineralogist is the peer-reviewed journal of the Mineralogical Society of America , a non-profit association. It publishes original scientific research in the general fields of mineralogy, crystallography, geochemistry, and petrology....
noted that bursaite's X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
data shows many coincidences between those of the minerals kobellite and cosalite. However, later studies showed that bursaite's characteristics are nearly identical to the mineral lillianite's.
Bursaite's X-ray diffraction pattern is nearly identical to that of lillianite's, with only slightly more peaks than lillianite. This was eventually explained as a mixture
Mixture
In chemistry, a mixture is a material system made up by two or more different substances which are mixed together but are not combined chemically...
of two orthorhombic phases
Phase (matter)
In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...
in the mineral. The two phases in bursaite unlike those in lillianite are two Bbmm phases that appear to be exsolution products of phase III, which is simply the synthetic analogue of lillianite. Given this information, it was inferred that bursaite is an intergrowth of two sulfosalt phases, derived from lillianite.