PRETULITE, SCPO4, A NEW SCANDIUM MINERAL FROM THE STYRIAN AND LOWER AUSTRIAN LAZULITE OCCURRENCES, AUSTRIA

Pretulite is a new Sc phosphate with zircon-type structure from the ph yllite-micaschist hosted hydrothermal lazulite-quartz veins in the Low er Austroalpine Grobgneis complex, eastern Austria. The new species is the Sc-dominant analogue of xenotime-(Y) and occurs as an accessory m ineral in all investigated lazulite specimens, forming anhedral to euh edral crystals up to 200 mu m long with the dominant form {211}. It is associated with lazulite, fluorapatite, chlorapatite, quartz, muscovi te, clinochlore, paragonite, kyanite, pyrophyllite, augelite, wardite, hydroxylherderite, goyazite, florencite-(Ce), xenotime-(Y), bearthite , rutile, pyrite, corundum, and an AlO(OH)-phase. Pretulite is translu cent to transparent with an adamantine luster, colorless to pale pink, uniaxial positive with omega = 1.790 (5), epsilon = 1.86 (1) and show s a weak orange fluorescence at 254 nm as well, as a bright blue catho doluminescence. Mohs hardness is about 5. The empirical formula for pr etulite (based on four O atoms) is (Sc0.98Y0.02)(1.00)P1.00O4.00. It c ontains variable amounts of Y with Y/(Y + Sc) = 0.5 - 3.2 mol% and tra ces of Yb, Er, and Dy. The space group is I4(1)/amd with a = 6.589 (1) Angstrom, c = 5.806 (1) Angstrom, V = 252.1 (1) Angstrom(3), d(calc) = 3.71 g/cm(3), Z = 4. The four strongest lines in the X-ray powder pa ttern are d(200) = 3.293 (100), d(112) = 2.4636 (42), d(312) = 1.6927 (45), d(332) = 1.3697 (15) Angstrom. The crystal structure was refined using 108 reflections to R(F-0) = 0.018. Cell parameters and average M-O distances confirm a small amount of Y substituting Sc in the eight fold-coordinated M-position. The formation of pretulite is attributed to a moderate enrichment of Sc in lazulite-rich domains of the veins ( about 180 ppm) and the inability of the accompanying minerals to incor porate larger quantities of Sc in their crystal structure. The name is after the mountain Pretul, Fischbacher Alpen, Styria, Austria.