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Formula: CaB6O9(OH)2.3H2O
Hydrated hexaborate
Crystal System: Monoclinic
Specific gravity: 2.09 measured, 2.098 calculated
Hardness: 3
Streak: White
Colour: Colourless, white
Luminescence: Not fluorescent under UV
Solubility: Slightly soluble in cold water, moderately soluble in hot water, dissolves readily in cold dilute acids and
strong alkalies, slowly soluble in a 30 per cent solution of hydrogen peroxide, in xylol, and in glyerol, very slightly
soluble in methyl alcohol. Nobleite reacts with dilute sulphuric acid to produce crystals of
gypsum and boric acid.
Localities
At El Tatio geothermal field, El Loa Province, Antofagasta, Chile, teruggite is
the dominant phase in a soft, off-white, poorly-layered and weakly-cemented surface crust, 10–15 mm thick, occurring in
the high-temperature geothermal field. Other minerals present include halite,
which is present throughout but also forms a thin (<0.5 mm), brittle, cratered surface to the deposit, nobleite,
ulexite and opal-A, with possible traces of
illite-smectite and at least one
unidentified phase
(AM 46.560–571).
At the type locality, Unnamed Nobleite locality [1], Ryan, Furnace Creek Mining District, Inyo County, California, USA,
nobleite has been found at seven places that are widely spaced for twelve miles along virtually the length of the
area containing borates between the floor of Death valley and the Widow Mines in
the Greenwater Range south of Ryan. The nobleite is associated with other
borate minerals produced by the weathering of
colemanite and priceite veins in
altered olivine basalt and
basaltic clastic rocks. Nobleite generally is in surficial, weathered
material on and near the source veins. The weathered matrix now consists chiefly of
montmorillonite, analcime and
some magnetite; along with borate
minerals it contains some gypsum,
thénardite, a manganese oxide
mineral and limonite. The newly formed
borates in surficial material at nobleite localities include
ulexite, gowerite,
meyerhofferite, colemanite, an
undescribed calcium borate, a magnesium
borate, ginorite and
sassolite. An apparently exceptional occurrence of the mostly coarsely
crystalline nobleite was found in the Corkscrew mine. Two other occurrences in the Hard Scrabble claim and the
Widow No 3 mine are in efflorescences on mine workings in priceite- or
colemanite- bearing altered
basalt. At every locality where the original
colemanite or priceite veins are
exposed, some of the nobleite encrusts the veins, which generally show corrosion. A crust of
meyerhofferite in one specimen lies between the
colemanite and some of the nobleite. Clusters of
gowerite crystals are attached to nobleite aggregates and some of this
gowerite in turn supports individual crystals of nobleite. An
undescribed calcium borate at one place fills in between the microblades of
gowerite on the nobleite. Much of the nobleite forms a coherent
open meshwork of tabular crystals, commonly intergrown with fluffy ulexite, an
undescribed manganese oxide, or doubly terminated microcrystals of
colemanite. Like closely associated
ginorite and sassolite, clots of
euhedral nobleite are also irregularly spaced through a nearly coherent matrix of weathered
basaltic surficial debris. Some of the
ginorite is interspersed among the larger crystals of nobleite, coating
them and filling in between as if at least this ginorite formed later than this
nobleite.
The largest best-formed crystals of nobleite were obtained from the Corkscrew mine, where they were found on
colemanite in several geodelike cavities which were joined by small fissures.
The lower cavity was entirely coated with nobleite, while the upper cavities were only partially covered. The
crystals range in size from less than 1 mm to more than 3 mm. There were only two minerals in direct contact with the
nobleite, colemanite and
ulexite
(AM 46.560-571).
Nobleite from the Corkscrew Canyon Mine -
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