Adamite

Adamite is a secondary mineral that forms in oxidation environments of zinc and arsenic deposits, typically in arid zones where meteoric water has altered primary minerals. The crystals, which can reach significant sizes, display a vitreous luster and transparency that make them particularly sought after by mineralogists. The most celebrated variety is the emerald green adamite from Tsumeb in Namibia, while fluorescent blue specimens have been found in Mexico and Peru.

Adamite formation typically occurs in association with other oxidation zone minerals such as limonite, malachite, and calcite. Its relative fragility (hardness 3.5 on the Mohs scale) makes it delicate to handle, but this characteristic does not diminish its scientific and collectible value. Some specimens exhibit ultraviolet fluorescence, glowing an intense yellow-green under long-wave UV light.

Adamite — Zn₂(AsO₄)(OH). Crystal system: orthorhombic, space group Pnma. Lattice parameters: a = 8.48 Å, b = 7.47 Å, c = 6.03 Å. Hardness: 3.5 Mohs. Density: 4.32–4.35 g/cm³. Refractive index: nα = 1.704, nβ = 1.743, nγ = 1.763; birefringence: 0.059 (biaxial positive). Cleavage: perfect along plane 101. Color: emerald green, yellow, blue, colorless; white streak. Luster: vitreous. Transparency: transparent to translucent.

Raman spectroscopy: characteristic bands attributed to vibration modes of AsO₄ groups (around 800–900 cm⁻¹) and OH (3300–3500 cm⁻¹). UV fluorescence: yellow-green under long-wave (365 nm), sometimes absent or weak. Thermal analysis: loss of structural water between 300–400 °C. Mineral associations: limonite, goethite, malachite, calcite, smithsonite, olivenite. Genesis: oxidation zone mineral in zinc and arsenic deposits in arid environments.