Analcime

Analcime
Analcime with aegirine and natrolite from Mont Saint-Hilaire, Québec (size: 78 x 65 x 53 mm)
General
Category	Zeolite
Formula (repeating unit)	NaAlSi2O6·H2O
Strunz classification	9.GB.05
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Ibca
Identification
Color	White, colorless, gray, pink, greenish, yellowish
Crystal habit	Typically in crystals, usually trapezohedrons, also massive to granular.
Twinning	Polysynthetic on [001], [110]
Cleavage	Very poor [100]
Fracture	Uneven to subconchoidal
Mohs scale hardness	5 - 5.5
Luster	Vitreous
Streak	White
Specific gravity	2.24 - 2.29
Optical properties	Isotropic; anomalously biaxial (-)
Refractive index	n = 1.479 - 1.493
Fusibility	3.5
Other characteristics	Weakly piezoelectric; weakly electrostatic when rubbed or heated.
References

Analcime or analcite (from the Greek analkimos - "weak") is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi₂O₆·H₂O. Minor amounts of potassium and calcium substitute for sodium. A silver-bearing synthetic variety also exists (Ag-analcite).

Analcime is usually classified as a zeolite mineral, but structurally and chemically it is more similar to the feldspathoids. Analcime occurs as a primary mineral in analcime basalt and other alkaline igneous rocks. It also occurs as cavity and vesicle fillings associated with prehnite, calcite, and zeolites.

Well known locations for sourcing analcime include Croft Quarry in Leicestershire, UK; the Cyclopean Islands east off Sicily and near Trentino in northern Italy; Victoria in Australia; Kerguelen Island in the Indian Ocean; in the Lake Superior copper district of Michigan, Bergen Hill, New Jersey, Golden, Colorado, and at Searles Lake, California in the United States; and at Cape Blomidon, Nova Scotia and Mont Saint-Hilaire, Quebec in Canada; and in Iceland.