Compound sulphate, ettringite group
Specific gravity: 1.881
Colour: Colourless, white
Thaumasite is a very late-stage mineral in some sulphide ore deposits, formed in
contact metamorphic zones and from the reaction of
geothermal waters or seawaters with basalt and
tuff. Associated minerals include
calcite, gypsum and
At Eddy Creek quarry, Weld river, southern Tasmania, Australia, thaumasite has been found in a skarn deposit (AJM 18.1.65).
At the Francon quarry, Quebec, Canada, thaumasite has been found on fracture surfaces in a highly weathered serpentine-bearing dike (MinRec 37.1.47).
In the Deccan traps of India, thaumasite has been found as a fibrous aggregate on scolecite (MinRec 34.1.63).
At Crestmore, Riverside county, California, USA, thaumasite occurs with spurrite, ettringite or monticellite (Dana) in spurrite - merwinite - gehlenite skarn (AM 48.1394-1396).
At the Braen quarry, Passaic county, New Jersey, USA, thaumasite occurs in both datolite and quartz pockets in the pillow basalt. On some specimens thaumasite can be seen alongside unaltered gypsum (MinRec 40.6.520).
At West Paterson and great Notch, Passaic county, New Jersey, USA, thaumasite is sometimes pseudomorphous after anhydrite (Dana).
Common impurities: Al,Fe,Mg
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