Cupalite

Cupalite
General
Category	Native element class, alloy
Chemical formula	(Cu,Zn,Fe)Al
Strunz classification	01.AA.20
Identification
Color	Steel-gray yellow
Crystal system	Orthorhombic
Mohs scale hardness	4-4.5
Luster	Metallic
Specific gravity	5.12 g/cm3
Other characteristics	non-magnetic, non-radioactive
References	[1][2]

Cupalite is a rare mineral which is mostly composed of copper and aluminium, but might contain up to several percents of zinc or iron;^[3] its chemical structure is therefore described by an approximate formula (Cu,Zn)Al or (Cu,Fe)Al. It was discovered in 1985 in placers derived from serpentine, in association with another rare mineral khatyrkite (CuAl₂). Both minerals are thus far restricted to the area of Listvenitovyi Stream, in the Khatyrka ultramafic (silicon-poor) zone of the Koryak–Kamchatka fold area, Koryak Mountains, Beringovsky District, Chukotka Autonomous Okrug, Far Eastern Federal District, Russia.^[4] The mineral name derives from cuprum (Latin for copper) and aluminium. Its holotype (defining sample) is preserved in the Mining Museum in Saint Petersburg, and parts of it can be found in other museums, such as Museo di Storia Naturale di Firenze.^[1][2][3]

Properties

Cupalite forms dendritic, rounded or irregular grains, typically below 0.1 millimeter in size, which are intergrown with khatyrkite. They have an orthorhombic crystal structure with a yet uncertain space group and the lattice constants a = 0.695(1) nm, b = 0.416(1) nm, c = 1.004(1) nm, and 10 formula units per unit cell. Their Mohs hardness is between 4 and 4.5 and Vickers hardness is in the range 272–318 kg/mm² for a 20–50 gram load.^[5]

Cupalite and khatyrkite are accompanied by spinel, corundum, stishovite, augite, forsteritic olivine, diopsidic clinopyroxene and several Al-Cu-Fe metal alloy minerals. They are remarkable by containing micrometre-sized grains of the only known naturally occurring quasicrystal – aperiodic, yet ordered structure. The quasicrystal has a composition of Al₆₃Cu₂₄Fe₁₃ and icosahedral symmetry. The presence of unoxidized aluminium in cupalite and association with the stishovite – a form of quartz which forms exclusively at high pressures of several tens GPa – suggest that cupalite is formed either upon meteoritic impact or in the deep earth mantle.^[3][6]

References

1. ^ ^{a b} "Cupalite". Mineral Data Publishing. http://www.handbookofmineralogy.org/pdfs/cupalite.pdf. Retrieved 2009-08-07. 
2. ^ ^{a b} "Cupalite". Mindat.org. http://www.mindat.org/min-1171.html. Retrieved 2009-08-07. 
3. ^ ^{a b c} Steinhardt, Paul; Bindi, Luca (2010). "Once upon a time in Kamchatka: the search for natural quasicrystals". Philosophical Magazine: 1. doi:10.1080/14786435.2010.510457. http://www.physics.princeton.edu/~steinh/naturalquasicrystals.html. 
4. ^ Razin, L.V., N.S. Rudashevskii, and L.N. Vyal'sov. (1985) New natural intermetallic compounds of aluminum, copper and zinc – khatyrkite CuAI2, cupalite CuAI and zinc aluminides – from hyperbasites of dunite-harzburgite formation. Zap. Vses. Mineral. Obshch., 114,90–100 (in Russian). c.f. (1986) Amer. Mineral., 71, 1278
5. ^ Hawthorne, F. C. et al. (1986). "New Mineral Names". American Mineralogist 71: 1277–1282. http://rruff.info/uploads/AM71_1277.pdf. 
6. ^ Bindi, Luca; Paul J. Steinhardt, Nan Yao, Peter J. Lu (2009-06-05). "Natural Quasicrystals". Science 324 (5932): 1306–9. Bibcode 2009Sci...324.1306B. doi:10.1126/science.1170827. PMID 19498165. http://www.physics.princeton.edu/~steinh/naturalquasicrystals.html. Retrieved 2009-08-07. Lay summary.