Ashburtonite

Ashburtonite is a rare lead copper silicate-bicarbonate mineral with formula: HPb₄Cu²⁺₄Si₄O₁₂(HCO₃)₄(OH)₄Cl.^[5]

Ashburtonite
General
Category	Cyclosilicates
Formula (repeating unit)	HPb4Cu4Si4O12(HCO3)4(OH)4Cl
IMA symbol	Ahb[1]
Strunz classification	9.CF.05
Crystal system	Tetragonal
Crystal class	Dipyramidal (4/m) H-M symbol: (4/m)
Space group	I4/m
Unit cell	a = 14.23, c = 6.1 [Å]; Z = 2
Identification
Color	Blue
Crystal habit	Prismatic, needle like in clusters
Cleavage	None
Fracture	Conchoidal
Tenacity	Brittle
Luster	Vitreous to adamantine
Streak	light blue
Diaphaneity	Transparent
Specific gravity	Greater than 4.07, calculated 4.69
Optical properties	Uniaxial (+)
Refractive index	nω = 1.786 nε = 1.800
Birefringence	0.0140
References	[2][3][4][5]

Geological occurrence

Ashburtonite was first described as a secondary mineral in a shear zone in a series of shales and graywackes. It is an alteration product of galena and chalcopyrite.^[4] The secondary minerals within the shear consist of carbonates, arsenates, and sulfates of lead and copper, and to a much lesser extent of zinc and iron.^[5] Ashburtonite is associated with beudantite, brochantite, caledonite, cerussite, diaboleite, duftite, malachite, plattnerite, adamite, antlerite, bayldonite, bindheimite, carminite, chenevixite, chlorargyrite, chrysocolla, cinnabar, hemimorphite, hydrozincite, jarosite, lavendulan, linarite, mimetite, olivenite, paratacamite, and rosasite.

Ashburtonite was first described in 1991 for an occurrence in the Anticline prospects 11 km (6.8 mi) southwest of Ashburton Downs in the Capricorn Range of Western Australia.^[4] It has also been reported from the Tonopah–Belmont Mine in the Big Horn Mountains of Maricopa County, Arizona.^[3]

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Webmineral
3. Mindat
4. Handbook of Mineralogy
5. Grice, J. D.; Nickel, E. H.; Gault, R. A. (1991). "Ahsburtonite, a new bicarbonate-silicate mineral from Ashburton Downs, Western Australia: Description and structure determination" (PDF). American Mineralogist. 76: 1701–1707.