Adamite: Occurrence and Physical Properties

Adamite is a zinc arsenate hydroxide mineral, Zn₂AsO₄OH. It occurs in many different lively colors. It is a mineral that typically occurs in the oxidized or weathered zone above zinc ore occurrences. Different impurities are responsible for the color types. Pure adamite is colorless, but usually it possess yellow color due to Fe compounds admixture. When copper is present in Adamite, this gives a vibrant green or blue color, and when cobalt is present, it gives a pink to purple color. Some impurities such as copper prevent the Adamite from its habit of being fluorescent. 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.

General Information:

Category: Arsenate mineral
Formula: Zn₂AsO₄OH
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

Occurrence

Named to honor French mineralogist Gilbert-Joseph Adam who supplied the first samples. Adamite is an uncommon secondary mineral that can be found in oxidized zinc and arsenic bearing hydrothermal deposits.

It 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.

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.

Physical Properties of Adamite

Lustre: Vitreous, Sub-Vitreous, Waxy, Greasy
Transparency: Transparent, Translucent
Color: Ideally white, colorless, frequently pale yellow, honey-yellow, brownish yellow, rose red; blue, pale green to green, may be zoned; bright green (cuprian); bright pink, purple (cobaltian)
Comment: colourless or faintly tinted in transmitted light.
Streak: white
Hardness: 3½ on Mohs scale
Hardness Data: Measured
Tenacity: Very brittle
Cleavage: Distinct/Good on {101}, good; on {010}, poor.
Fracture: Irregular/Uneven, Conchoidal
Density: 4.32 – 4.48 g/cm³ (Measured), 4.435 g/cm³ (Calculated)

Adamite crystals are usually embedded in rusting, crumbly, brown Limonite matrix that stain the hands. Since the Limonite crumbles when scrubbed, care must be exercised when washing such specimens.

Information Source: