Conichalcite

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Conichalcite
Conichalcite.jpg
A thin crust of conichalcite on a rock.
General
Category Arsenate minerals
Formula
(repeating unit)
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[edit]

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[edit]

  1. ^ a b c Mindat.org
  2. ^ a b c Handbook of Mineralogy