Outstanding colorless crystals of the extremely rare arsenate-phosphate-sulphate mineral machatschkiite from the type and only known locality worldwide in Anton mine, Germany. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Machatschkiite
Machatschkiite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Ca₆(AsO₄)(AsO₃OH)₃(PO₄)·15H₂O.
It crystallizes in the hexagonal crystal system (space group R3c).
Key properties: Mohs hardness 2–3; specific gravity 2.5–2.6; optically uniaxial.
IMA symbol Mct, IMA status: approved, named in 1976.
Found as a very rare secondary mineral in crusts on granite.
It is found associated with Picropharmacolite, pharmacolite, cobaltian sainfeldite, gypsum.
The mineral was named to honor Felix Karl Ludwig Machatschki (1895–1970), Professor of Mineralogy, University of Vienna, Vienna, Austria.