Kristiansenite, a new calcium-scandium-tin sorosilicate from granite pegmatite in Tordal, Telemark, Norway

Kristiansenite occurs as a late hydrothermal mineral in vugs in an amazonite pegmatite at Heftetjern, Tordal, Telemark, Norway. Tapering crystals, rarely up to 2 mm long, are colourless, white, or slightly yellowish. The mineral has the ideal composition Ca2ScSn(Si2O7)(Si2O6OH) and is triclinic C1 with cell parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) A, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, V = 1062.7(3) A3 (Z = 4). It has a monoclinic cell within ∼ 0.1 A and is polysynthetically twinned on {010} by metric merohedry. The strongest reflections in the X-ray powder pattern are [d in A, (I obs), (hkl)]: 5.18 (53) (1–11), 3.146 (100) (004), 3.089 (63) (−222), 2.901 (19) (221), 2.595 (34) (222), 2.142 (17) (−3–31). The Mohs’ hardness is 5½–6; Dcalc. = 3.64 g/cm3; only a mean refractive index of 1.74 could be measured. Scandium enrichment in the Heftetjern pegmatite and the crystal chemistry of scandium are briefly discussed.