Kröhnkite
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Kröhnkite is a rare copper sulfate mineral named after B. Kröhnke who first researched it. Kröhnkite may be replaced by Saranchinaite, the anhydrous form of the mineral, if heated to temperatures above 200 °C. Wikipedia
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Encrustations (on matrix), fibrous, massive
Crystal system: Monoclinic
Formula (repeating unit): Na2Cu(SO4)2•2H2O
Optical properties: Biaxial (-)