Bursaite is a

sulfosalt Sulfosalt minerals are sulfide minerals with the general formula , 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 ...

of the lillianite family. It has the formula Pb₅Bi₄S₁₁ and

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

structure. Bursaite is named after

Bursa Province Bursa Province ( tr, ) is a province in Turkey along the Sea of Marmara coast in northwestern Anatolia. It borders Balıkesir to the west, Kütahya to the south, Bilecik and Sakarya to the east, Kocaeli to the northeast and Yalova to the nor ...

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...

, where it was discovered.Rasit, T. (1954-55
A study on the concentration tests and beneficiation of the Uludag tungsten ore
. Bull. Mineral Research and Exploralion Inst. Turkey, Foreign Ed., No. 46-47, 106-127. It is generally located in regions rich in

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

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 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. ( ...

s under intense heating.Borodaev, Y., Garavelli, A., Garbarino, C, Grillo, S, Mozgova, N, Uspenskaya, T. A Rare Sulfosalts from Volcano. (2001) The Canadian Mineralogist, 39 1383-1396. 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

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or Dolomite (mineral), dolomite. Marble is typically not Foliation (geology), foliated (layered), although there are exceptions. In geology, the ...

s and

granites Granite () is a coarse-grained (phaneritic) intrusive igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedime ...

amidst the

Uludağ Uludağ (), the ancient Mysian or Bithynian Olympus (Greek: Όλυμπος), is a mountain in Bursa Province, Turkey, with an elevation of . In Turkish, ''Uludağ'' means "great mountain". In ancient times the range of which it is a part, ext ...

massif in Bursa, Western Turkey, by scientist Rasit Tolun in 1955. Tolun was also the first to study the

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...

composition of bursaite via flotation and superpanner tests. It was originally tested as an aggregate of a larger sulfosalt

specimen Specimen may refer to: Science and technology * Sample (material), a limited quantity of something which is intended to be similar to and represent a larger amount * Biological specimen or biospecimen, an organic specimen held by a biorepository ...

. The flotation test involved

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

-based

reagents In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

and oils. The specimen was also chemically analyzed via

X-ray spectroscopy X-ray spectroscopy is a general term for several spectroscopic techniques for characterization of materials by using x-ray radiation. Characteristic X-ray spectroscopy When an electron from the inner shell of an atom is excited by the energy o ...

and contained 4.24%

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...

, 4.78% blende, 5.48%

bismuth Bismuth is a chemical element with the Symbol (chemistry), symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental ...

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

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

, dipyramidal mineral. Its symmetry is 2/m2/m2/m,

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 unchan ...

''Bbmm''.Anthony, J.W., Bideaux, R., Bladh, K., Nichols, M. Bursaite. (2003) Mineral Data Publishing. It was once believed to be

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 ...

due to its high reflective power and its oblique extinction.Fleischer, M. (1956
New Mineral Names
American Mineralogist, 41 671. The mineral contains ionic bonding between its

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

and

sites. Given the mineral's plate-like

habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

, 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 = These numbers yield an axial ratio a:b:c = 0.3078:1:1.5331. The mineral displays strong

pleochroism Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgroun ...

and weak anisotropy.

Physical properties

Bursaite has a tabular, plate-like

habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

. It is composed of many prismatic

crystals A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosc ...

, which generally form along the 00axis, 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 Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...

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 is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefring ...

is generally weak in air, but stronger when bursaite is immersed in

oils An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

. Bursaite has a hardness of 2.5 on the

Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

. 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.Fleischer, M. (1972
New Mineral Names
American Mineralogist, 57 325-329.

Occurrence

Like many sulfosalts, bursaite occurs in

regions In geography, regions, otherwise referred to as zones, lands or territories, are areas that are broadly divided by physical characteristics (physical geography), human impact characteristics (human geography), and the interaction of humanity and t ...

abundant in sulfur. Close to its discovery grounds, it commonly occurs in Uludağ, Turkey, around a metamorphic scheelite deposit near Bursa. It is also associated with the

sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...

veinlets around the Shumilovsk deposit in

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

, the volcanogenic massive Cofer deposit in

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

, and the

American Southwest The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, N ...

. It also occurs

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

Lipari Islands Lipari (; scn, Lìpari) is the largest of the Aeolian Islands in the Tyrrhenian Sea off the northern coast of Sicily, southern Italy; it is also the name of the island's main town and ''comune'', which is administratively part of the Metropolit ...

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

and

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

. Bursaite commonly occurs alongside other sulfosalts, such as

sphalerite Sphalerite (sometimes spelled sphaelerite) is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimen ...

, pyrite, chalcopyrite, bismuth and

scheelite Scheelite is a calcium tungstate mineral with the chemical formula Ca W O4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist K. Scheele (1742-1786). Well-formed crystals are sought by collectors a ...

. 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 Mineralogist ''American Mineralogist: An International Journal of Earth and Planetary Materials'' is a peer-reviewed scientific journal covering the general fields of mineralogy, crystallography, geochemistry, and petrology. It is an official journal of the Min ...

noted that bursaite's

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

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 X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

pattern is nearly identical to that of lillianite's, with only slightly more peaks than lillianite. This was eventually explained as a

mixture In chemistry, a mixture is a material made up of two or more different chemical substances which are not chemically bonded. A mixture is the physical combination of two or more substances in which the identities are retained and are mixed in the ...

of two orthorhombic phases in the mineral.Jambor, J., Burke, E. (1989
New Mineral Names

, 74 1399-1404. The two phases in bursaite unlike those in lillianite are two ''Bbmm'' phases that appear to be

exsolution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

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.Neues Jahrb. (1988) Mineral, Abh. 158

References

{{reflist, 30em

External links

Entry on mindat.orgEntry on webmineral.comBursaite entry in the Handbook of Mineralogy
Sulfosalt minerals Orthorhombic minerals Minerals in space group 63