Formula: Na0.3Fe3+2(Si,Al)4O10(OH)2.nH2O phyllosilicate
Specific Gravity: 2.06 to 2.32
Hardness: 1 to 2
Streak: White
Colour: Green, olive-green, yellow-green, yellow, orange, brown

Volcanic igneous environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Nontronite is a weathering product of basalt and other mafic and ultra-mafic volcanic rocks. It also occurs in poorly drained volcanic ash soils, in some hydrothermally altered mineral deposits, and contact metamorphosed limestone. It is authigenic (formed in place) in recent marine sediments. It is formed in the presence of both neutral and acid cool hydrothermal fluids, and is stable up to about 140oC.

Common impurities: Ti,Mg,Ca

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