Class: Carbonates (Nitrates)
A common secondary mineral formed in the oxidation zone of copper deposits; locally may be an ore of copper (
Anthony et al., 2001—2005).
Original description: unknown [prehistoric].
Type locality: unknown [prehistoric].
Type material: unknown.
Etymology: named in antiquity after the Greek μαλαχή (malachi), mallows, in allusion to its green colour.
Distribution: Australia; Congo; France; Namibia; Russia: Ural Mountains; USA (
Anthony et al., 2001—2005).
Chemistry
Cu2(CO3)(OH)2
Essential elements: hydrogen (H), carbon (C), oxygen (O), copper (Cu).
Crystal data
Crystallography: monoclinic — prismatic.
Crystal habit: crystals are acicular to prismatic, thick tabular, equant, with {100}, {010}, {001}, {110}, {201}, several other forms, rounded, in sprays and crude composite aggregates, to 9 cm; botryoidal.
Twinning: on {100}, {201}, very common as contact or penetration twins, also polysynthetic (
Anthony et al., 2001—2005).
Optical properties
Colour: bright green, dark green, commonly banded in masses; green to yellowish green in transmitted light (
Anthony et al., 2001—2005).
Diaphaneity: translucent to opaque (
Anthony et al., 2001—2005).
Lustre: adamantine to vitreous; silky if fibrous; dull if massive (
Anthony et al., 2001—2005).
Refractive index: 1.655—1.909 — anisotropic [biaxial (-)] (
Arem, 1987: 127).
Birefringence: 0.25—0.254.
Dispersion: none.
Pleochroism: none.
Material from ‘Repository’
3 specimens: 0625 — 4.05 ct, Madagascar;
0626 — 6.67 ct, Madagascar;
0603 — 3.80 ct, Democratic Republic of the Congo.
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