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Formula: Ca6Fe3+2(SO4)2.5[B(OH)4](OH)12.25H2O
Compound sulphate, ettringite group
Crystal System: Trigonal
Specific gravity: 1.847 measured, 1.855 calculated
Hardness: 2½
Streak: Pale yellow, greenish yellow, brownish orange (altered)
Colour: Bright Yellow to amber
Environments
Metamorphic environments
Hydrothermal environments
Sturmanite is an uncommon secondary mineral occurring in
cavities in metamorphosed bedded manganese deposits, associated with baryte,
manganite, hausmannite and
hematite
(HOM).
Localities
At the type locality, the Black Rock mine, near Kuruman, Northern Cape, South Africa, sturmanite
pseudomorphs after baryte and
after gypsum have been found
(KL p194, 195). Associated minerals include baryte and
hematite
(Dana).
At the NChwaning mine, Kalahari manganese fields, South Africa, rhodochrosite
pseudomorphs after sturmanite have been found
(KL p164).
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