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Formula: CaMg[B3O4(OH)3]22O
Hydrated borate containing hydroxyl
Crystal System: Monoclinic
Specific gravity: 2.15 to 2.17 measured, 2.170 calculated
Hardness: 2
Streak: White
Colour: Colourless, white
Solubility: Virtually insoluble in cold water, partially dissolved by prolonged submersion in boiling water
Environments
Hydroboracite typically is formed by groundwater alteration of colemanite, or it may be
primary. Associated minerals include
colemanite and tunellite
(HOM).
Localities
At Penobsquis, Cardwell Parish, Kings county, New Brunswick, Canada, hydroboracite is very common as crystals to 2 cm in length, usually
associated with volkovskite, hilgardite and
trembathite. It may be cavernous with large fluid or solid inclusions of
boracite, clay and
mica. Strontioginorite has been observed impaling
hydroboracite
(CM 43.1469-1487).
At the Salt Springs evaporite deposit, Hammond Parish, Kings county, New Brunswick, Canada, boracite,
the major borate mineral, occurs in association with hydroboracite, hilgardite,
szaibélyite, priceite,
ulexite, colemanite and
danburite.
Halite has been found in one intersection as soft, chalky white nodules to 1 mm, associated with
boracite and hydroboracite
(CM 19.291-301).
At the Gharah Gol Boron mine, Dandi, Mahneshan County, Zanjan, Iran, the major mineral is hydroboracite, with minor presence of other
borates such as colemanite, inyoite,
meyerhofferite and szaibélyite. The
hydroboracite is mostly massive, but microcrystals are quite common. Yellow to yellowish-brown and rarely reddish-brown crystals of
colemanite to 3 cm have been found. They most likely formed as a later stage mineral after some
of the hydroboracite was dissolved
(R&M 92.6.542-544).
The type locality is the Inder B deposit and salt dome, Inder, Atyrau Region, Kazakhstan.
At Boulby mine, Loftus, Redcar and Cleveland, England, UK, hydroboracite has been found in core samples from the evaporites as glassy
beige crystals to 0.7 cm in length associated with salmon-orangepink volkovskite crystals and
frosted grey-white boracite microcrystals. Szaibélyite
occurs intimately associated with volkovskite, boracite,
hilgardite and hydroboracite
(R&M 91.5.434-441).
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