Althausite is a relatively simple magnesium phosphate mineral with formula Mg2(PO4)(OH,F). It is very rare. Original occurrences are magnesite deposits among serpentinites. It is named after Egon Althaus (born 1933), a mineralogist at the University of Karlsruhe, Germany.(from Wikipedia)
The hardness is 3.5. Occcur as lustrous bright blocky violet-brownish crystal aggregates, very rich in a pale brownish-grey Magnesite-Clinochlore matrix. A rare high-pressure Magnesium-Phosphate from Overntjern Quarry, Overntjern, Modum, Buskerud / Norway.
Size: 7.4x7.4x5 mm.
Weight: 1.82 ct.