Nontronite

Formula: Na_0.3Fe₂(Si,Al)₄O₁₀(OH)₂.nH₂O

Origin of name: after locality Nontron, Saint Pardoux, France

Crystal system: monoclinic

Crystal class: unknown

Twinning: 

Unit cell: 

Colour: pale yellow to olive-green

Diaphaneity: nearly opaque

Luster: dull to somewhat resinous or waxy

Habit: massive, fine-grained, clay-like

Hardness: 1 to 2

Specific gravity: 2 to 3

Cleavage: 1; {001} perfect

Tenacity: 

Streak: 

Synonyms/varieties:

Comments: member of the smectite group (clay)