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Formula: CaSrB5O9Cl.H2O
Hydrated pentaborate,
hilgardite group,
strontium-bearing mineral
Crystal System: Triclinic
Specific gravity: 2.99 measured, 3.04 calculated
Hardness: 6 to 6½
Streak: White
Colour: Colourless to white
Environments
In 1952 kurgantaite was described as a new mineral, in 1982 it was discredited as a
strontium-bearing variety of
tyretskite, and in 2000 it was revalidated and approved by the IMA.
Localities
At Penobsquis, Cardwell Parish, Kings county, New Brunswick, Canada, the marine evaporites consist of an early carbonate
unit, followed by a sulphate, and finally, a salt unit. The borate assemblages
occur in specific beds of halite and
sylvite that were the last units to form in the evaporite sequence. Species
identified from drill-core sections include boracite,
brianroulstonite,
chambersite, colemanite,
congolite, danburite,
hilgardite, howlite,
hydroboracite, kurgantaite,
penobsquisite, pringleite,
ruitenbergite,
strontioginorite,
szaibélyite, trembathite,
veatchite, volkovskite and
walkerite. In addition, 41 non-borate
species have been identified, including magnesite,
monohydrocalcite, sellaite,
kieserite and fluorite.
At Penobsquis, there is an upper unit of hilgardite +
volkovskite + trembathite in
halite and a lower unit of
hydroboracite + volkovskite +
trembathite–congolite in
halite–sylvite. Values of the ratio of
boron isotopes are consistent with a seawater source, without any need for a
more exotic interpretation. The assemblage is consistent with a fore-basin deposition by evaporation
(CM 43.1469-1487).
At the type locality, Mt Kurgan-tau, Inder B deposit and salt dome, Inder District, Atyrau Region, Kazakhstan,
kurgantaite occurs as fine-grained nodules up to 4 cm across, in the borate
deposit.
(Mindat).
Associated minerals include sylvite,
halite, boracite,
anhydrite, gypsum,
magnesite and quartz
(HOM)
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