Adamite

Adamite
Yellow-green adamite in limonite
General
Category	Arsenate mineral
Formula (repeating unit)	Zn2AsO4OH
IMA symbol	Ad[1]
Strunz classification	8.BB.30
Dana classification	41.06.06.03 Olivenite group
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H–M symbol: (2/m 2/m 2/m)
Space group	Pnnm
Identification
Color	Pale yellow, honey-yellow, brownish yellow, reddish; rarely white, colorless, blue, pale green to green, may be zoned
Crystal habit	Wedge-like prisms typically in druses and radiating clusters; also smooth botryoidal masses
Cleavage	{101}, good; {010}, poor
Fracture	Uneven to subconchoidal
Tenacity	Brittle
Mohs scale hardness	3.5
Luster	Vitreous
Streak	White to pale green
Specific gravity	4.32–4.48 measured
Optical properties	Biaxial (+/−)
Refractive index	nα=1.708 – 1.722, nβ=1.742 – 1.744, nγ=1.763 – 1.773
Birefringence	δ = 0.055
Other characteristics	May fluoresce and phosphoresce lemon-yellow under SW and LW UV.
References	[2][3][4]

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.