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Formula: BaSi2O5.4H2O
Inosilicate (chain silicate), multiple chains, barium-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 2.66 measured, 2.76 calculated
Hardness: 2 to 3
Streak: White
Colour: White to colourless
Luminescence: Not fluorescent under UV
Common impurities: Ca,Sr,Na
Environments
Bigcreekite has been found filling fractures in gneiss near the
margins of a granodiorite pluton. Associated minerals include
sanbornite, quartz,
diopside and pyrrhotite
(HOM).
Localities
At the type locality, the Esquire No. 7 claim, Big Creek, Big Creek-Rush Creek Mining District, Fresno County,
California, USA, bigcreekite fills very thin (<0.5 mm) transverse fractures in
gneissic rocks composed of variable amounts of
sanbornite and quartz, with
minor amounts of diopside,
pyrrhotite and barium-bearing
minerals. The rocks form conformable tabular bodies up to 13 m thick within foliated
quartzite at or within 100 m of the contact with a
granodiorite pluton. The Big Creek site is the type locality for
alforsite and walstromite
and is known for several rare minerals including anandite,
bazirite, benitoite,
celsian, gillespite,
fresnoite, muirite,
macdonaldite, pellyite,
titantaramellite and
verplanckite
(CM 39.3.761-768).
Bigcreekite from the Esquire No. 7 Claim -
Image
At Trumbull Peak Ba-silicate deposit, Trumbull Peak, Clearing House, Clearing House Mining District, East Belt,
Mariposa County, California, USA, bigcreekite also has been found filling thin fractures in
barium silicate lenses exposed along the northwestern slope of Trumbull Peak.
The Trumbull Peak barium silicate site is the type locality for
sanbornite and is known for several rare minerals including
alforsite, celsian,
gillespite, macdonaldite,
pellyite,
titantaramellite and
witherite. Additional minerals identified from these
barium-rich lenses include
benitoite, fresnoite,
kinoshitalite and
walstromite
(CM 39.3.761-768).
At both localities, Big Creek and Trumbull Peak, bigcreekite formed during or after the fracturing of the
barium silicate rocks. It postdates the host rock, and may represent either
a later primary phase deposited from infiltrating fluids or a
product of alteration of a pre-existing barium-rich mineral, possibly
sanbornite. The barium silicate
rocks probably originated from sedimentary units that were metamorphosed prior to being uplifted to their present
position. The mineral assemblages in these rocks are probably related to the initial bulk composition of the
sedimentary rocks prior to metamorphism. It has been suggested that
sanbornite was formed by the reaction of
witherite with quartz, and that
the sanbornite quartz rocks
formed at temperatures between 440 and 600°C
(CM 39.3.761-768).
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