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Formula: Ca4MgB4O6(CO3)2(OH)6
Compound borate
Crystal System: Monoclinic
Specific gravity: 2.77 measured, 2.765 calculated
Hardness: 4
Streak: White
Colour: Greenish-blue to bluish green, nearly colourless
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the Fuka mine, Fuka, Bitchū, Takahashi City, Okayama Prefecture, Japan, borcarite is a rare
secondary mineral probably formed by reaction of late
hydrothermal fluids with brucite. Associated minerals include
olshanskyite,
bultfonteinite, takedaite
and calcite
(HOM).
Borcarite from Fuka - Image
At Charcas, Charcas Municipality, San Luis Potosí, Mexico,
the primary minerals are
sphalerite, galena,
chalcopyrite, bornite,
tetrahedrite,
arsenopyrite, pyrite and
silver minerals such as jalpaite,
diaphorite and acanthite. In
the host rock, as metamorphic or alteration minerals, danburite,
datolite, hedenbergite,
epidote, chlorite,
andradite, actinolite
and wollastonite have been reported.
Quartz, calcite and
danburite crystallised during the entire life of the systems, throughout
the intrusive emplacement, metamorphism, and mineralising events. With depth, both
sphalerite and galena decrease
while chalcopyrite increases.
Secondary sulphides formed include
bornite, covellite,
digenite and chalcocite.
Native silver, native gold,
hematite and goethite were
deposited after the sulphides
(Minrec 55.6.727-728).
Borcarite has only recently (2019) been recognized at Charcas; it occurs as large crystal aggregates and
individual crystals of a greenish blue to bluish green to dark brown colour, in some cases at least partially
transparent. Blue crystals are often found overgrown on darker ones. Crystals are prismatic with size ranging from
less than 1 mm to 1.2 cm. Associated minerals include nifontovite,
calcite and (with the darker crystals) granular
andradite crystals to 2 mm; beige crystals of
cahnite on borcarite have also been identified. Small
borcarite lots are emerging from time to time from the San Bartolo mine. The thumbnails consist of lone,
loose crystals to 1 cm and crystal groups with little or no matrix. The crystals are tabular, lustrous, transparent,
pale to medium blue-green, and reach 1 cm in size
(Minrec 55.6.735-736).
Borarite from Charcas - Image
At the Type Locality, the Snezhnoe B ore occurrence, Izvestkovyi Stream, Titovskoe B deposit, Tas-Khayakhtakh Range,
Dogdo River Basin, Polar Yakutia, Sakha Republic, Russia, borcarite occurs in
kotoite marble, formed in
dolostone near the contact with
granodiorite. The borcarite forms dense masses up to 0.5 m
in diameter and as veins in kotoite
marble and in
ludwigite-szaibélyite-magnetite
rock. It contains inclusions of szaibélyite,
calcite, serpentine,
magnetite and spinel
(AM 50.2097). Other associated minerals include uralborite,
sibirskite and kotoite
(HOM).
Borcarite from Snezhnoe - Image
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