Nontronite is a sodium ferric-iron silicate hydroxide hydrate mineral of the clay group. Nontronites chemical formula is Na0.3Fe+++2(Si,Al)4O10(OH)2·n(H2O). It — Photo: Shannon Heinle · CC0
Nontronite
The iron-rich smectite clay — an olive-green 'iron bentonite' of weathered basalts and seafloor vents.
Intro adapted from Wikipedia (CC BY-SA).
Nontronite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₀.₃Fe³⁺₂(Si,Al)₄O₁₀(OH)₂·nH₂O.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Clay, Smectite-vermiculite structural group.
Key properties: Mohs hardness 1.5–2; specific gravity 2.2–2.3; typically green or yellow or brown; greenish-white streak; Waxy, resinous, dull luster; refractive index 1.576; optically biaxial.
IMA symbol Non, IMA status: approved, named in 1827.
A weathering product of basalts, kimberlites, and other ultramafic igneous rocks; in poorly-drained volcanic ash soils; in some hydrothermally altered mineral deposits, mido cean ridge basalts, and contact metamorphosed limestones.
It is found associated with Quartz, \opal, " \hornblende, " pyroxenes, olivine, mica, kaolinite.
The name refers to the occurrence near Saint-Pardoux, Nontron Arrondissement, France.
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