Sauconite

Formula: Na_0.3Zn₃(Si,Al)₄O₁₀(OH)₂.nH₂O

Origin of name: after locality Upper Saucon, Lehigh County, Pennsylvania, USA

Crystal system: monoclinic

Crystal class: unknown

Twinning:

Unit cell: 

Colour: reddish brown, mottled brownish yellow

Diaphaneity: 

Luster: dull

Habit: micaceous plates, minute, in parallel aggregates, massive, very fine-grained, clay-like

Hardness: 1 to 2

Specific gravity: 

Cleavage: 1; {001} perfect

Tenacity: 

Streak: 

Synonyms/varieties:

Comments: member of the smectite group (clay)