Offrétite

Formula: (K₂,Ca)₅Al₁₀Si₂₆O₇₂.30H₂O

Origin of name: for A. Offret, French professor

Crystal system: hexagonal

Crystal class: -6m2

Twinning: 

Unit cell: a = 13.29 Å, c = 7.582 Å

Colour: colourless to white

Diaphaneity: 

Luster: vitreous

Habit: crystals prismatic, vertically striated, rounded, minute, hemispherical with radiating structure

Hardness: 4

Specific gravity: 2.13

Cleavage: 1; {0001} distinct

Tenacity: uneven, brittle

Streak: 

Synonyms/varieties:

Comments: