Thortveitite and associated Sc-bearing minerals from Ravalli County, Montana

The rare Sc mineral thortveitite, (Sc,Y)2Si2O7, occurs as ??m- to mm-sized crystals in fluorite-bearing granitic pegmatites and the host melagabbro within the Crystal Mountain fluorite deposit, Ravalli County, Montana. Thortveitite is found as colorless and clear to smoky and translucent, subhedral to euhedral prisms up to 3 mm in length in the massive fluroite, as mm-sized anhedra to subhedra in diopside and edenite, and as ??m-sized droplet-like crystals in actinolite. Micrometric textures suggest that some thortveitite exsolved from actinolite, which contains between 1.2 and 2.9 wt.% Sc2O3. The source of the Sc is believed to be magmatic. The physical, optical and crystallographic properties of thortveitite are described. -from Authors