- Conichalcite
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Conichalcite 
A thin crust of conichalcite on a rock.General Category Arsenate minerals Chemical formula CaCu(AsO4)(OH) Strunz classification 08.BH.35 Dana classification 41.5.1.2 Crystal symmetry Orthorhombic (2 2 2) - disphenoidal Unit cell a = 7.39(1) Å, b = 9.23(1) Å, c = 5.83(1) Å; V 397.66 ų; Z = 4 Identification Color Grass-green to yellowish green, pistachio-green, emerald-green; may be zoned Crystal habit Crusts of acicular to almost fibrous crystals. Also as botryoidal masses and compact crusts. Crystal system Orthorhombic Twinning Rare on {001} Cleavage Absent Fracture Uneven Tenacity Brittle Mohs scale hardness 4.5 Luster Vitreous, greasy Streak Green Diaphaneity Translucent Specific gravity 4.3 Optical properties Biaxial (+/-) Refractive index nα = 1.778 - 1.800 nβ = 1.795 - 1.831 nγ = 1.801 - 1.846 Birefringence δ = 0.023 - 0.046 Pleochroism Visible Dispersion Strong r < v to r < v moderate References [1][2] Conichalcite, CaCu(AsO4)(OH), is a relatively common arsenate mineral related to duftite (PbCu(AsO4)(OH)). It is green, often botryoidal, and occurs in the oxidation zone of some metal deposits. It occurs with limonite, malachite, beudantite, adamite, cuproadamite, olivenite and smithsonite.[1][2]
Formation
Mat of conichalcite spheres on limonite base from the Ojuela Mine, Mapimí, Durango, Mexico (size: 10.4 x 8.9 x 4.2 cm)
Conichalcite forms in the oxidation zones of copper orebodies. Here groundwater enriched with oxygen react with copper sulfide and copper oxide to produce an array of minerals such as malachite, azurite and linarite. Conichalcite is often found encrusted on to limonitic rocks that have yellow to red colors.
Conichalcite will also form a solid solution series with the mineral calciovolborthite. When these two minerals form a solid solution series, the two interchanging elements are arsenic and vanadium. Conichalcite is the arsenic rich end member of the series and calciovolborthite is the vanadium rich end member.[1]
Notable occurrences of conichalcite include Juab Co., Utah; Lincoln and Lyon counties of Nevada and Bisbee, Arizona, in the USA; Durango, Mexico; Collahuasi, Tarapaca, Chile; Calstock, Cornwall and Caldbeck Fells, Cumbria, England; Andalusia, Spain; and Tsumeb, Namibia.[2]
References
- ^ a b c Mindat.org
- ^ a b c Handbook of Mineralogy
Categories:- Arsenate minerals
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