Analcime

Formula:  NaAlSi₂O₆^.H₂O

Origin of name:  From Greek for weak, alluding to the weak eletrostatic charge developed when heated or rubbed

Crystal system:  Cubic

Crystal class:  4/m -3 2/m

Twinning:  on {001} or {110}, polysynthetic

Unit cell:  a = 13.72 Å

Colour:  Colourless, white, gray, yellowish, pink

Diaphaneity: Transparent to translucent

Luster:  Vitreous

Habit:  Crystals usually well-formed trapezohedrons or modified cubes; massive granular

Hardness: 5 to 5.5

Specific gravity:  2.24 to 2.29

Cleavage:  1; {100} very poor

Tenacity:  Brittle

Streak: White

Synonyms/varieties:  Analcite, Analcidite

Comments:  Series with pollucite. Member of the zeolite group. Weakly piezoelectric. Found in the groundmass or vesicles of silica-poor intermediate and mafic igneous rocks, typically basalts and phonolites, from late-stage hydrothermal solutions, or disseminated due to deuteric alteration. In lake beds, altered from pyroclastics or clay, as a primary precipitate; authigenic in sandstones and siltstones