Olivenite

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Olivenite
Mineraly.sk - olivenit.jpg
General
Category Arsenate minerals
Formula
(repeating unit)
Cu2AsO4OH
Strunz classification 08.BB.30
Dana classification 41.06.06.01
Identification
Color Olive green to yellow or brown, gray-green, grayish white
Crystal habit Fibrous, globular and reniform; granular, earthy, massive
Crystal system Monoclinic - Prismatic 2/m
Twinning On {010}
Cleavage {101}, {110}, indistinct
Fracture Conchoidal to irregular
Mohs scale hardness 3
Luster Adamantine to vitreous, pearly to silky if fibrous
Streak Olive-green to brown
Diaphaneity Translucent to opaque
Specific gravity 4.46
Optical properties Biaxial (+/-)
Refractive index nα = 1.747 - 1.780 nβ = 1.788 - 1.820 nγ = 1.829 - 1.865
Birefringence δ = 0.082 - 0.085
Pleochroism Weak green and yellow
2V angle Measured: 80° to 90°, Calculated: 46° to 84°
Dispersion strong r > v or r < v
References [1][2][3]

Olivenite is a copper arsenate mineral, formula Cu2AsO4OH. It crystallizes in the monoclinic system (pseudo-orthorhombic),[1] and is sometimes found in small brilliant crystals of simple prismatic habit terminated by domal faces. More commonly, it occurs as globular aggregates of acicular crystals, these fibrous forms often having a velvety lustre; sometimes it is lamellar in structure, or soft and earthy.

A characteristic feature, and one to which the name alludes (German, Olivenerz, of A. G. Werner, 1789), is the olive-green color, which varies in shade from blackish-green in the crystals to almost white in the finely fibrous variety known as woodcopper. The hardness is 3, and the specific gravity is 4.3. The mineral was formerly found in some abundance, associated with limonite and quartz, in the upper workings in the copper mines of the St Day district in Cornwall; also near Redruth, and in the Tintic Mining District in Utah. It is a mineral of secondary origin, a result of the oxidation of copper ores and arsenopyrite.

The arsenic of olivenite is sometimes partly replaced by a small amount of phosphorus, and in the species libethenite we have the corresponding copper phosphate Cu2PO4OH. This is found as small dark green crystals resembling olivenite at Libethen in the Slovak Republic, and in small amount also in Cornwall. Other members of this isomorphous group of minerals are adamite, Zn2AsO4OH, and eveite, Mn2AsO4OH.

Olivenite from Mammoth Mine, Tintic, Utah

References[edit]