Bursaite

{{Infobox mineral | name = Bursaite | category = Sulfosalt mineral | boxwidth = | boxbgcolor = | image = | imagesize = | alt = | caption = | formula = Pb5Bi4S11 | molweight = 2177.65 g/mol | strunz = 2.JB.40a | system = Orthorhombic Intergrowth of two sulfosalts | dana = | color = Gray to white | colour = | habit = Prismatic crystals with platy, long grains | symmetry = Bbmm | twinning = Lamellar twinning on (001), sometimes (110) plane | cleavage = Tabular on (100) - good | fracture = | tenacity = | mohs = 2.5 - 3 | luster = Metallic | streak = | diaphaneity = | gravity = | density = 6.2 g/cm3 (calculated) | polish = | opticalprop = Opaque; strong anisotropy | refractive = | birefringence = Weak in air, stronger in oil. | pleochroism = Weak; whitish blue to brownish gray | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = Not radioactive | alteration = | references = <ref name="Tolun"/><ref name="Anthony"/><ref name="Kraeff">Kraeff, A. (1973) [http://www.mta.gov.tr/english/dergi/dergi_pdf/82/8.pdf Reflectance Values And Microhardness Tests of Bursaite] {{Webarchive|url=https://web.archive.org/web/20110717134711/http://www.mta.gov.tr/english/dergi/dergi_pdf/82/8.pdf |date=2011-07-17 }}. Mineral Research and Exploration Institute of Turkey, Ankara.</ref> }}

'''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.<ref name="Tolun">Rasit, T. (1954-55) [http://www.mta.gov.tr/english/dergi/dergi_pdf/46-47/8.pdf A study on the concentration tests and beneficiation of the Uludag tungsten ore] {{Webarchive|url=https://web.archive.org/web/20110717134638/http://www.mta.gov.tr/english/dergi/dergi_pdf/46-47/8.pdf |date=2011-07-17 }}. Bull. Mineral Research and Exploralion Inst. Turkey, Foreign Ed., No. 46-47, 106-127.</ref> 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 minerals under intense heating.<ref name="Borodaev">Borodaev, Y., Garavelli, A., Garbarino, C, Grillo, S, Mozgova, N, Uspenskaya, T. A Rare Sulfosalts from Volcano. (2001) The Canadian Mineralogist, 39 1383-1396.</ref> It was officially delisted as a mineral in 2006, being cited as an intergrowth of two other sulfosalts.<ref name="Burke">{{cite journal|author=Burke, E.|title=A Mass Discreditation of GQN Minerals|year=2006|journal=The Canadian Mineralogist|volume=44|issue=6|pages=1557–1560|doi=10.2113/gscanmin.44.6.1557|url=http://pubsites.uws.edu.au/ima-cnmnc/GQNminerals.pdf|access-date=2009-12-02|archive-url=https://web.archive.org/web/20120326091801/http://pubsites.uws.edu.au/ima-cnmnc/GQNminerals.pdf|archive-date=2012-03-26|url-status=dead}}</ref>

==History== Bursaite was discovered in a contact zone between a set of marbles and granites amidst the Uludağ massif in Bursa, Western Turkey, by scientist Rasit Tolun in 1955.<ref name="Tolun"/> 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.<ref name="Tolun"/>

Bursaite is named after the Bursa Province of Turkey where it was discovered.<ref name="Tolun"/> After much discussion of bursaite's credibility as a mineral,<ref name="Jambor"/> it was eventually delisted as part of a mass discreditation of minerals.<ref name="Burke"/>

==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 group ''Bbmm''.<ref name="Anthony">Anthony, J.W., Bideaux, R., Bladh, K., Nichols, M. Bursaite. (2003) Mineral Data Publishing.</ref> It was once believed to be monoclinic due to its high reflective power and its oblique extinction.<ref name="Fleischer 1">Fleischer, M. (1956) [http://www.minsocam.org/ammin/AM41/AM41_671.pdf New Mineral Names]. American Mineralogist, 41 671.</ref>

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.<ref name="Anthony"/> The mineral displays strong pleochroism and weak anisotropy.<ref name="Fleischer 1"/>

==Physical properties== Bursaite has a tabular, plate-like habit. 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.<ref name="Anthony"/>

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.<ref name="Anthony"/> Many hand samples of bursaite appear to be nearly identical to the mineral lillianite.<ref name="Borodaev"/>

In a microscope, bursauite shows distinct high reflective power and oblique extinction.<ref name="Fleischer 1"/> 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.<ref name="Kraeff"/>

Bursaite has a hardness of 2.5 on the Mohs scale. It has a gray, metallic luster that appears white in polished sections.<ref name="Anthony"/> The mineral is also known to have good tabular cleavage along the (100) planes.<ref name="Fleischer_2">Fleischer, M. (1972) [http://www.minsocam.org/ammin/AM57/AM57_325.pdf New Mineral Names]. American Mineralogist, 57 325-329.</ref>

==Occurrence== Like many sulfosalts, bursaite occurs in regions 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 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.<ref name="Anthony"/>

Bursaite commonly occurs alongside other sulfosalts, such as sphalerite, pyrite, chalcopyrite, bismuth and scheelite.<ref name="Fleischer 1"/> 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.<ref name="Borodaev"/>

==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.<ref name="Burke"/> Bursaite's status as a mineral was questioned almost from the time of its discovery. In 1956, Michael Fleischer of the American Mineralogist noted that bursaite's X-ray data shows many coincidences between those of the minerals kobellite and cosalite.<ref name="Fleischer 1"/> However, later studies showed that bursaite's characteristics are nearly identical to the mineral lillianite's.<ref name="Borodaev"/>

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.<ref name="Jambor">Jambor, J., Burke, E. (1989) [http://ammin.geoscienceworld.org/cgi/content/abstract/74/11-12/1399 New Mineral Names]. American Mineralogist, 74 1399-1404.</ref> 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.<ref name="Borodaev"/> Given this information, it was inferred that bursaite is an intergrowth of two sulfosalt phases, derived from lillianite.<ref name="Neues">Neues Jahrb. (1988) Mineral, Abh. 158</ref>

==References== {{reflist|30em}}

==External links== *[http://www.mindat.org/min-807.html Entry on mindat.org] *[http://webmineral.com/data/Bursaite.shtml Entry on webmineral.com] *[http://www.handbookofmineralogy.org/pdfs/BURSAITE.pdf Bursaite entry in the Handbook of Mineralogy]

Category:Sulfosalt minerals Category:Orthorhombic minerals Category:Minerals in space group 63