GeoPicture of the Week: Carminite

It’s been a while since we posted a mineral for our #GeoPicture section, and now we’re back with a special one: carminite. Carminite is a rare, special mineral with small crystals (usually smaller than 2cm) which often occur as acicular crystals. The mineral is heavy but soft and interestingly enough, despite being really beautiful, it forms as an alteration product of arsenopyrite (FeAsS) in the oxidized zones of some lead-bearing deposits.

There is no observed piezoelectric effect associated with carminite. The mineral is slowly soluble in hydrochloric acid (HCl). The chemical formula is (brace yourself) PbFe³⁺₂(AsO₄)₂(OH)₂).