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Formula: CaMn2+4Si5O14(OH)2.H2O
Inosilicate (chain silicate), manganese-bearing mineral
Crystal System: Triclinic
Specific gravity: 3.31 measured, 3.379 calculated
Hardness: 6½
Streak: Very pale pink
Colour: Pink to reddish orange, brown
Solubility: Insoluble or only very slightly soluble in hot concentrated acids
Common impurities: Al,Fe,Ni,Co,Mg,Na
Environments
Santaclaraite dehydrates to bustamite at about
550oC in air
(AM 69.200-206).
Localities
The type locality, the Pennsylvania mine, Sugarloaf Mountain, Black Wonder Mining District, Santa Clara county,
California, USA, is one of about fifty abandoned manganese mines
located in Santa Clara that occur in chert. The paragenesis of the
specimens is noteworthy in that the more common manganese minerals are
scarce or absent and the manganese silicates so far found are all
unusual in some respects. Santaclaraite occurs both as cross-fibre veins (the largest measures 1 cm in
width by more than 9 cm in length) and irregular masses (10 cm in maximum dimension) in manganese oxide stained
chert and quartz.
Santaclaraite is the most abundant manganese silicate at this
locality. Manganese-rich
howieite is associated with santaclaraite as yellow-brown
fibrous veinlets, masses and small spherules. Fine-grained
rhodochrosite is subordinate to the
manganese silicates but is widely disseminated throughout them and
the quartz matrix.
Kutnohorite and calcium-bearing
rhodochrosite were found in a single occurrence as small
scalenohedra to 0.6 mm.
The manganese mineral that was mined at this locality appears to have
been braunite, which occurs as masses and veins, up to 6 cm across.
Other associated minerals are calcite (some
manganoan), baryte, rare
harmotome, chalcopyrite
and native copper. Some of the
quartz is coloured dark greyish blue by inclusions of asbestiform
riebeckite
(AM 69.200-206).
At the Buckeye mine, Mount Oso, Ladd-Buckeye Mining District, Stanislaus county, California, USA,
santaclaraite occurs sparsely as pink prismatic crystals up to 3 mm long in
quartz veins in tan chert,
associated with rhodochrosite, a
friedelite-like mineral,
braunite, and very minor
chalcopyrite
(AM 69.200-206).
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