Fluorannite

fluorannite

zircon

fluorite

magnetite

Images

Formula: KFe2+3(Si3Al)O10sF2
Phyllosilicate (sheet silicate), biotite group, F may be replaced by OH, leading to annite
Crystal System: Monoclinic
Specific gravity: 3.16 to 3.20 measured, 3.23 calculated
Hardness: 3
Streak: Grey
Colour: Iron-black
Luminescence: Not fluorescent
Environments

Igneous environments

Localities

At the type locality, the Western suburb, Suzhou City, Suzhou, Jiangsu, China, fluorannite occurs as euhedral to subhedral sheets and tabular crystals to more than 6 mm across, but predominantly 2 to 4 mm long and 1 to 3 mm wide. Iron-black colour, submetallic lustre, with a grey streak. The mineral is a rock-forming species in the upper part of an A-type granite (AM 86.1534-1537). Associated Minerals include quartz, zircon, fluorite and magnetite (Mindat).

At the SK Star #2 Mining Claim, The Cove, Topaz Mountain, Thomas Range, Juab County, Utah, USA, topaz occurs in rhyolite. The topaz is typically black in colour because of numerous dark inclusions, but sherry-coloured, grey and colourless topaz crystals are also occasionally found. Analysis of thin sections of inclusions in the topaz indicates the presence of tungsten-rich ixiolite, magnetite, fluorite and fluorannite. Calcium-fluorine-rich fluid inclusions were also observed. The fluorannite occurs with fluorite and zircon in magnesium-deficient igneous rocks (MinRec 51.6.809-810).

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