Adamite

Adamite is a zinc arsenate hydroxide mineral, Zn2AsO4OH. It is a mineral that typically occurs in the oxidized or weathered zone above zinc ore occurrences. Pure adamite is colorless, but usually it possess yellow color due to Fe compounds admixture. Tints of green also occur and are connected with copper substitutions in the mineral structure. Olivenite is a copper arsenate that is isostructural with adamite and there is considerable substitution between zinc and copper resulting in an intermediate called cuproadamite. Zincolivenite is a recently discovered mineral being an intermediate mineral with formula CuZn(AsO4)(OH). Manganese, cobalt, and nickel also substitute in the structure. An analogous zinc phosphate, tarbuttite, is known.

Adamite on limonite from the Gold Hill District Tooele County, Utah, USA - Scale at bottom is approx. 2.5 cm.
This article is about the mineral. For the religious sect, see Adamites.
Adamite
Yellow-green adamite in limonite
General
CategoryArsenate mineral
Formula
(repeating unit)		Zn2AsO4OH
Strunz classification8.BB.30
Dana classification41.06.06.03
Olivenite group
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPnnm
Identification
ColorPale yellow, honey-yellow, brownish yellow, reddish; rarely white, colorless, blue, pale green to green, may be zoned;
Crystal habitWedge-like prisms typically in druses and radiating clusters - also smooth botryoidal masses.
Cleavage{101}, good; {010}, poor
FractureUneven to subconchoidal
TenacityBrittle
Mohs scale hardness3.5
LusterVitreous
Streakwhite to pale green
Specific gravity4.32–4.48 measured
Optical propertiesBiaxial (+/-)
Refractive indexnα=1.708 - 1.722, nβ=1.742 - 1.744, nγ=1.763 - 1.773
Birefringenceδ = 0.055
Other characteristicsMay fluoresce and phosphoresce lemon-yellow under SW and LW UV
References[1][2][3]

Occurrence

Adamite occurs as a secondary mineral in the oxidized zone of zinc- and arsenic-bearing hydrothermal mineral deposits. It occurs in association with smithsonite, hemimorphite, scorodite, olivenite, calcite, quartz and iron and manganese oxides.[1]

The yellow to bright lime-green colored crystals and druze along with its distinctive fluorescence make adamite a favorite among mineral collectors. Found in Mapimí, Durango, Mexico; Greece; and California and Utah in the United States.

Adamite was named after the French mineralogist Gilbert-Joseph Adam (1795–1881). It was first described in 1866 for an occurrence at the type locality of Chañarcillo, Copiapó Province, Atacama Region, Chile.[2]

See also

References
  1. http://rruff.geo.arizona.edu/doclib/hom/adamite.pdf Handbook of Mineralogy
  2. http://www.mindat.org/min-21.html Mindat.org
  3. http://webmineral.com/data/Adamite.shtml Webmineral data
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