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Formula: Ca3B5O6(OH)7Cl2.8H2O
Hydrated pentaborate
Crystal System: Monoclinic
Specific gravity: 1.97 measured, 1.93 calculated
Hardness: 5
Streak: White
Colour: Colourless to white
Luminescence: Not fluorescent under long wave or short wave UV
Environments
At the type locality, the Potash Corporation of Saskatchewan Mine, Penobsquis, Cardwell Parish, Kings county, New
Brunswick, Canada, Brianroulstonite was discovered in a piece of drill core from the lower third of the Upper
Halite member within a thick sequence of evaporites. The list of borate minerals
includes boracite, veatchite,
colemanite,
danburite, hilgardite-1A,
hilgardite-4M, howlite,
hydroboracite, priceite,
szaibélyite, ulexite,
volkovskite, pringleite,
ruitenbergite, trembathite,
strontioginorite, congolite,
tyretskite, ginorite,
inyoite and penobsquisite. Other
minerals found with the
borate assemblage include anhydrite,
sellaite, fluorite,
nickeline, pyrite,
chalcopyrite, sphalerite,
halite, sylvite,
microcline, diopside,
quartz, a mica group mineral, a
clay mineral, hematite,
limonite, magnesite,
calcite, dolomite,
monohydrocalcite and
malachite. Organic material is present in several sections of core.
Brianroulstonite is intimately associated with halite,
hilgardite, pringleite,
trembathite, sellaite,
fluorite, hematite,
muscovite, penobsquisite and a
clay-group mineral. Only a few cleavage masses, with a total approximate
mass of 10 mg, were separated.
Brianroulstonite occurs as cleavable masses to 2 X 1 X 1 mm3, with individual crystals of micaceous
habit approximately 0.5 x 0.25 X 0.1 mm3 in size. The thin colourless to white lamellae are flexible,
transparent to translucent,
with a vitreous lustre and a white steak
(CM 35.3.751-758).
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