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Formula: Mg2[B6O7(OH)6]2.9H2O
Hydrated hexaborate
Crystal System: Trigonal
Specific gravity: 1.867 measured, 1.866 calculated
Hardness: 2½
Streak: White
Colour: Colourless, white
Luminescence: Pale yellow fluorescence under UV
Solubility: Slowly soluble in water
Environments
Localities
At the Tincalayu Mine, Antofagasta de la Sierra Department, Catamarca Province, Argentina, mcallisterite occurs
as a primary mineral in a metamorphosed
borate playa deposit, associated with
rivadavite
(HOM).
At the Da Qaidam salt lake, Da Qaidam, Haixi Mongol and Tibetan Autonomous Prefecture, Qinghai, China,
mcallisterite occurs associated with hexahydrite,
hydroboracite and
hungchaoite
(HOM).
At the type locality, the Mott prospect, Twenty Mule Team Canyon, Furnace Creek Mining District, Inyo County,
California, USA, the first macallisterite collected occurred as a very minor constituent of an efflorescent
layer between colemanite and
priceite-bearing shale and a
surface crust of powdery clay on a steep hillside at the prospect.
The prospect was opened because of the borate minerals present, essentially
colemanite and priceite. The
mcallisterite occurred very sparingly in a pale yellowish brown matrix of
sassolite and clay with closely
associated small white pellets of ginorite.
Mcallisterite is closely associated with other boron minerals,
particularly ginorite and sassolite.
Many of the snow-white pellets, initially believed to be pure mcallisterite, were found to be intimate mixtures
with ginorite. Occasionally, small glassy clusters of sugary crystals
more than a millimeter across are encountered. Most of the mcallisterite is in small rounded pellets generally a
millimetre or two in size, though occasionally clusters of pellets extend for a centimetre or so. The white pellets,
and some may be called snow-white, stand out prominently from their tawny coloured matrix of
sassolite and clay.
Mcallisterite is the eighth boron mineral from the weathered
colemanite and priceite veins in
the altered olivine basalts of
the area. Other boron minerals are
ulexite, hydroboracite,
gowerite, nobleite,
ginorite, meyerhofferite and
sassolite.
The minute crystals of mcallisterite, mostly much less than a millimetre across, are colourless (unless stained
by clay) and occasionally show a rhombohedral development in their faces.
The natural crystals are larger than the closely associated crystals of
ginorite but smaller than the associated plates of
sassolite
(AM 50.629-640).
Mcallisterite from Furnace Creek -
Image
At the Sterling Mine, Sterling Hill, Ogdensburg, Sussex County, New Jersey, USA, mcallisterite is associated
with starkeyite and gypsum
(HOM).
Mcallisterite from the Sterling Mine - Image
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