Loomisite

loomisite

dondoellite

earlshannonite

mitridatite

Images

Formula: Ba[Be₂P₂O₈].H₂O
Phosphate, beryllophosphate, barium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.46 measured, 3.512 calculated
Hardness: 3½ to 4
Streak: White
Colour: White
Solubility: Insoluble in water or hydrochloric acid
Environments

Pegmatites

Loomisite is a new mineral, approved in 2022 and to date (March 2023) reported only from the type locality.

Localities

At the type locality, the Big Chief mine (Johnson pegmatite), Glendale, Keystone Mining District, Pennington county, South Dakota, USA, loomisite was found in the granite pegmatite as divergent sprays of very thin bladed crystals with a tapered termination. Individual crystals are found up to 0.80 × 0.06 × 0.03 mm³. Associated minerals include dondoellite, earlshannonite, mitridatite, rockbridgeite, jahnsite-(CaMnFe) and quartz. Loomisite is murky white in transmitted light, transparent with white streak and silky to vitreous lustre (MM 87.1.79-85).

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