Pretulite  Bernhard, F., Walter, F., Ettinger, K., Taucher, J. & Mereiter, K. (1998): Pretulite, ScPO4, a new scandium mineral from the Styrian and Lower Austrian lazulite occurrences, Austria. American Mineralogist, 83, 625-630.

Abstract

Pretulite is a new Sc-phosphate with zircon-type structure from the phyllite-micaschist hosted hydrothermal lazulite-quartz veins in the Lower Austroalpine Grobgneis complex, eastern Austria. The new species is the Sc-dominant analogue of xenotime-(Y) and occurs as an accessory mineral in all investigated lazulite specimens, forming anhedral to euhedral crystals up to 200 mm long with the dominant form (211). It is associated with lazulite, fluorapatite, chlorapatite, quartz, muscovite, clinochlore, paragonite, kyanite, pyrophyllite, augelite, wardite, hydroxylherderite, goyazite, florencite-(Ce), xenotime-(Y), bearthite, rutile, pyrite, corundum, and an AlO(OH)-phase. Pretulite is translucent to transparent with an adamantine lustre, colorless to pale pink, uniaxial positive with w = 1.790 (5), e = 1.86 (1) and shows a weak orange fluorescence at 254 nm as well as a bright blue cathodoluminescence. Mohs hardness is ca. 5. The empirical formula for pretulite (based on four oxygens) is (Sc0.98Y0.02)1.00P1.00O4.00. It contains variable amounts of Y with Y/(Y+Sc) = 0.5-3.2 mol% and traces of Yb, Er and Dy. The space group is I41/amd with a = 6.589 (1) Å, c = 5.806 (1) Å, V = 252.1 (1) Å3, dcalc = 3.71 g/cm3, Z = 4. The strongest lines in the X-ray powder pattern are d200 = 3.293(100), d112 = 2.4636(42), d202 = 2.1777(14), d301 = 2.0546(14), d312 = 1.6927(45), d400 = 1.6470(14), d332 = 1.3697(15) Å. The crystal structure of pretulite was refined using 108 reflections to R(Fo) = 0.018. Cell parameters and average M-O distances confirm a small amount of Y substituting Sc in the eight-coordinated M-position. The formation of pretulite is interpreted to be due to a moderate enrichment of Sc in lazulite-rich domains of the veins (ca. 180 ppm) and the inability of the accompanying minerals to incorporate larger quantities of Sc in their crystal structure. The name is after the mountain Pretul, Fischbacher Alpen, Styria, Austria.
 


 
 
 
 
 
 
 

SEM-photograph of a distorted, euhedral pretulite crystal
with the dominant form (211), small (100) and rounded (111).
This crystal was used for structure refinement and is mounted
with epoxy. Sample HK1A (Höllkogel).
 


 
 
 
 
 
 
 
 

BSE-image of a sectioned pretulite grain, showing
chemical inhomogenity. Brighter areas are enriched
in Y, white areas are fluorapatite.
Sample HK1A (Höllkogel).
 

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