Althausite, a new mineral from Modum, Norway

Althausite occurs as cleavable masses in serpentine-magnesite deposits at Modum, Norway. The proposed formula in Mg2PO4 (OH0.37F0.25O0.10)0.81 with partly vacant halide sites. It is orthorhombic, space group Pna21, a = 8.258, b = 14.383, c = 6.054 A, Z = 8. D(meas)=2.97, ϱ(calc) = 2.91 g/cm3 (X-ray), ϱ(calc) = 3.06 g/cm3 (Gladstone-Dale), H = 3 12 −4. The strongest X-ray powder lines (41 given, FeKα radiation) with intensities and indices are 3.593 (100)(040), 3.316 (90)(211), 3.024 (80)(002), 2.786 (60)(112), 2641 (60)(122). The mineral is light grey with vitreous lustre, running brown on alteration to apatite. Non-fluorescent. Perfect cleavage {001}, distinct cleavage {101}. It is biaxial positive, α=1.588, β=1.592, γ=1.598, 2Vγ(calc)=78.5°, negative elongation, X=b, Y=c, Z=a. IR, DTA and TGA data are given.