Parasibirskite

parasibirskite

takedaite

olshanskyite

frolovite

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Formula: Ca2B2O5.H2O
Hydrated borate, paramorph of sibirskite
Specific gravity: 2.50 measured, 2.54 calculated
Hardness: 3
Streak: White
Colour: White
Environments

Metamorphic environments
Hydrothermal environments

Parasibirskite was approved in 1996, but to date (August 2022) it has been reported only from the type locality.

Localities

At the type locality, the Fuka mine, Fuka, Bitchū, Takahashi City, Okayama Prefecture, Japan, primary skarn minerals such as gehlenite and spurrite were formed as pyrometasomatic (Formed by metasomatic changes in rocks, principally in limestone, at or near intrusive contacts, under the influence of magmatic emanations and high to moderate temperature and pressure) products of limestone. In subsequent retrograde hydration reactions, most of the gehlenite crystals were altered to retrograde minerals such as vesuvianite, hydrogrossular and bicchulite. Retrograde changes of spurrite crystals, on the other hand, are not extensive.
During the post-metasomatic stage, an irregular vein consisting of borate minerals penetrated along the boundary between crystalline limestone and the skarns. In the vein, an anhydrous borate, takedaite, was primarily formed by the reaction of boron-bearing fluids with limestone. At the circumference of the vein, borates such as nifontovite, olshanskyite, frolovite and sibirskite were formed as secondary minerals by late hydrothermal alteration of takedaite.
Parasibirskite was found in the altered part of takedaite, and occurred as subparallel aggregates of tabular crystals up to 40 mm long, 20 mm wide and 3 mm thickness, in association with takedaite, olshanskyite, frolovite, sibirskite, pentahydroborite and calcite. It is likely that the parasibirskite also was formed by hydrothermal alteration of takedaite (MM 62.521-525).

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