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Formula: Mg2Al3B2O9(OH)
Borate
Crystal System: Monoclinic
Specific gravity: 3.508 calculated
Streak: White
Colour: Colourless
Environments
Localities
At the Stubenberg Quarry, Stubenberg am See, Hartberg-Fürstenfeld District, Styria, Austria, pseudosinhalite
and magnesiotaaffeite-6N′3S with rare lamellae of
magnesiotaaffeite-2N′2S occur as replacement products of
spinel in
geikielite–ilmenite–baddeleyite–zirconolite
veins within dolomite marble. The
crystallisation sequence of magnesium-aluminium phases is spinel →
pseudosinhalite → magnesiotaaffeite minerals, and
spinel formed after or during the replacement of
baddeleyite by zirconolite.
Pseudosinhalite contains up to 2.2 wt.% TiO2, 1.4% Cr2O3, and 1.3% FeO. The
replacement of
spinel by pseudosinhalite, a magnesium-aluminium
borate, requires an influx of boron, since
no boron-bearing minerals are present in the original assemblage
(CM 46.1195-1205).
At the type locality, the Tayezhnoe Fe-B skarn, Aldan, Sakha Republic, Russia, pseudosinhalite is a rare mineral
in a contact-metasomatic
boron-rich iron deposit, a product of
retrograde alteration of sinhalite in magnesium-bearing
skarn. Associated minerals include
calcite, dolomite,
forsterite, green spinel,
ludwigite, warwickite,
suanite, clinohumite,
szaibelyite, brucite,
sinhalite and hydrotalcite
(AM 84.1196-1197, HOM).
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