Cyanotrichite Crystals

Cyanotrichite is a wonderfully colored mineral. Its bright azure to sky blue color is very impressive. Cyanotrichite typically forms acicular or hair like crystals aggregated into radial clusters, tufts and sprays. The color is very impressive for such tiny crystals. It is an aptly named mineral since cyano and trich are derived from the Greek for blue and hair, respectively. It is formed from the oxidation of copper ore minerals along with other oxidation zone minerals.

Cyanotrichite is a hydrous copper aluminium sulfate mineral with formula Cu₄Al₂[(OH)₁₂|SO₄]·2H₂O, also known as lettsomite. Cyanotrichite forms velvety radial acicular crystal aggregates of extremely fine fibers.

It is an oxidation product of primary copper mineralization in a weathering environment with abundant aluminium and sulfate. Associated minerals include brochantite, spangolite, chalcophyllite, olivenite, tyrolite, parnauite, azurite and malachite.

Cyanotrichite Crystals. From Qinglong Mine, China.
Photo: © Matteo Chinellato

Formula: Cu4Al2(SO4)(OH)12 · 2H2O
Colour: Sky-blue, azure-blue
Lustre: Silky
Hardness: 1 - 3
Specific Gravity: 2.76
Crystal System: Orthorhombic
Streak is blue.
Associated Minerals are brochantite, smithsonite, malachite and azurite.
Notable Occurrences include Laurium, Greece; Leadhills, Scotland; Russia; South Africa; Arizona, Nevada and Utah, USA and France.
Best Field Indicators are crystal habit, associations and color.
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