Phyllosilicate (sheet silicate), smectite group
Specific Gravity: 2.06 to 2.32
Hardness: 1 to 2
Colour: Green, olive-green, yellow-green, yellow, orange, brown
Common impurities: Ti,Mg,Ca
Volcanic igneous environments
Nontronite is a weathering product of basalt,
kimberlite and other
mafic and ultra-mafic volcanic rocks. It also occurs in poorly drained
volcanic ash soils, in some hydrothermally altered mineral deposits, mid ocean ridge
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. Associated minerals include quartz,
mica and kaolinite
The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. nontronite is a secondary silicate that occurs as an alteration product of andradite (AJM 22.1.38).
The type locality is Le Manderau, Saint-Pardoux-la-Rivière, Nontron, Dordogne, Nouvelle-Aquitaine, France.
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, nontronite occurs as a massive alteration product of spodumene. The Emmons pegmatite is an example of a highly evolved boron-lithium-cesium-tantalum enriched pegmatite (R&M 94.6.512).
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