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Formula: NaCaB5O6(OH)6.5H2O
Borate
Crystal System: Triclinic
Specific gravity: 1.955 measured, 1.955 calculated
Hardness: 1 to 2½
Streak: White
Colour: Colourless, white
Luminescence: Fluorescent and some phosphorescence. Fluorescent yellow, greenish yellow, cream or white under UV
(Mindat)
Solubility: Slightly decomposed in cold water and more so in hot water, with the loss of Na to the solution
Environments:
Ulexite occurs typically as a secondary mineral in playa
and salt-marsh deposits in arid regions, and in bedded sedimentary deposits formed from these, the
boron being supplied from surrounding hot springs. Some occurrences contain
upwards of one billion tons of ulexite. Associated minerals include
colemanite,
borax, meyerhofferite,
hydroboracite, probertite,
glauberite, trona,
mirabilite, calcite,
gypsum and halite
(HOM).
Localities
At the Flat Bay Quarry, Newfoundland, Newfoundland and Labrador, Canada, the
anhydrite and gypsum beds contain small
quantities of ulexite and howlite. The ulexite occurs as irregular
patches 1-3 cm in diameter, consisting of white fibrous crystals. The normal amounts of
boron in seawater are sufficient to account for the observed quantity of borates
(CM 13.370-376).
At the type locality, Iquique Province, Tarapacá, Chile, ulexite occurs in playas in a desert region, associated
with pickeringite, nitratine,
halite and glauberite
(Mindat).
At the Jenifer Mine, U.S. Borax Mine, Kramer Borate deposit, Boron, Kern county, California, USA, strontium-bearing
ulexite was observed as veinlets on a specimen of bedded borax and
clay. The ulexite veins are up to 5 mm wide and irregularly separated by
borax altered on exposed surfaces to
tincalconite. Clay and
disseminated realgar are associated with both
borax and the ulexite. Discrete crystals of ulexite, some of which
are doubly terminated, are usually not longer than 0.5 mm
(AM 43.169-170).
At the Suckow borax mine, West Baker, Kramer Borate deposit, Boron, Kramer District,
Kern county, California, USA, ulexite was collected from the waste dump. It consists of small hand specimens of
white or transparent ulexite in a matrix of clay and
borax. The ulexite occurs as massive aggregates of crystalline grains,
irregularly distributed in the matrix. Some of the crystals are partially hollow, due to the inclusion, and subsequent
dissolving away, of small grains of borax. Most of the crystals are only a
fraction of a millimeter in length, although some reach a maximum of 6 mm
(AM 25.754-762).
At the Lang Mine, Tick Canyon Borate deposit, Tick Canyon, Lang, Los Angeles county, California, USA, fibrous white
ulexite occurs in association with colemanite,
howlite and calcite
(AM 3.35).
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