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Formula: Ca4Si6O17(H2O)2.(Ca.3H2O)
Phyllosilicate (sheet silicate), tobermorite group
Crystal System: Monoclinic
Specific gravity: 2.423 to 2.458 measured, 2.49 calculated
Hardness: 3
Streak: White
Colour: White, pinkish white
Common impurities: Al,Fe,Mg,Na,K,H2O
Environments:
Metamorphic environments
Hydrothermal environments
Basaltic cavities
Tobermorite is a hydrothermal alteration product of calcium carbonate rocks, due to
contact metamorphism,
and it is found filling vesicles and cavities in basalt
(HOM, Webmin).
Associated minerals include gyrolite,
natrolite, zeolites,
ettringite portlandite
and calcite
(Dana, HOM).
Localities
The type locality is Tobermory, Isle of Mull, Argyll and Bute, Scotland, UK.
At Crestmore, California, USA, tobermorite is associated with blue
calcite, monticellite
and vesuvianite
(Dana).
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