Olivenite

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Olivenite
Mineraly.sk - olivenit.jpg
General
CategoryArsenate minerals
Formula
(repeating unit)
Cu2AsO4OH
Strunz classification8.BB.30
Dana classification41.06.06.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/n
Identification
ColorOlive green to yellow or brown, gray-green, grayish white
Crystal habitFibrous, globular and reniform; granular, earthy, massive
TwinningOn {010}
Cleavage{101}, {110}, indistinct
FractureConchoidal to irregular
Mohs scale hardness3
LusterAdamantine to vitreous, pearly to silky if fibrous
StreakOlive-green to brown
DiaphaneityTranslucent to opaque
Specific gravity4.46
Optical propertiesBiaxial (+/-)
Refractive indexnα = 1.747 - 1.780 nβ = 1.788 - 1.820 nγ = 1.829 - 1.865
Birefringenceδ = 0.082 - 0.085
PleochroismWeak green and yellow
2V angleMeasured: 80° to 90°, Calculated: 46° to 84°
Dispersionstrong 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 luster; 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.

Olivenite from Mammoth Mine, Tintic, Utah

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 Ľubietová 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.

References[edit]

  •  This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Olivenite". Encyclopædia Britannica (11th ed.). Cambridge University Press.