Fillowite

fillowite

triploidite

fairfieldite

reddingite

Images

Formula: Na₂CaMn²⁺₇(PO₄)₆
Anhydrous phosphate, fillowite group, manganese-bearing mineral
Crystal System: Trigonal
Specific gravity: 3.43 measured, 3.48 calculated
Hardness: 4½
Streak: White
Colour: Greenish yellow to yellow green, yellowish brown, reddish brown; colourless; colourless to yellow in transmitted light
Solubility: Soluble in acids
Environments

Pegmatites

Fillowite is confined to a primary, high temperature pegmatite assemblage (AM 66.827-842 ).
At the type locality, the Fillow Quarry, Branchville, Redding, Fairfield County, Connecticut, USA, fillowite is a primary accessory mineral in a zoned granite pegmatite containing lithiophilite (HOM) associated with triploidite, fairfieldite and reddingite (HOM, Dana).
Image

On heating in air at 885^oC fillowite slowly changes to alluaudite (AM 50.1647-1669).

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