Multiple oxide, beryllium-bearing mineral
Specific gravity: 4.07 calculated
Hardness: 8 to 8½
Colour: Light green
Ferrotaaffeite-6N'3S is a very rare mineral that to date (February 2022) has been found only at the type locality.
At the type locality, the Rosendal pegmatite, Kimitoön Island, Kimitoön, Southwest Finland, the pegmatite was quarried mainly for K-feldspar and quartz; tantalum-bearing minerals and beryl were important by-products.
The pegmalite is a vertically dipping dyke in hornblende gabbro. Ferrotaaffeite-6N'3S occurs in the wall zone, which consists mainly of quartz, plagioclase, sillimanite, muscovite and spessartine-almandine garnet, with minor amounts of chlorite, biotite, epidote, allanite and calcite (CM.19.311-314 as pehrmanite, HOM). The ferrotaaffeite-6N'3S occurs as small, subhedral hexagonal tabular crystals up to 25O pm across and 40 microns thick (Mindat).
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