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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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