Analcime

Analcime
Reddish crystals of analcime up to 1.8 cm in size on matrix
General
Category	Zeolite
Formula (repeating unit)	NaAlSi2O6 · H2O
IMA symbol	Anl
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
Formula mass	220.15
Color	White, colorless, gray, pink, greenish, yellowish
Crystal habit	Typically in crystals, usually trapezohedrons, also massive to granular.
Twinning	Polysynthetic on [001], [110]
Cleavage	Indistinct on {001}, {010}, {100}
Fracture	Uneven to subconchoidal
Mohs scale hardness	5–5.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to subtransparent to translucent
Specific gravity	2.24–2.29
Optical properties	Isotropic; anomalously biaxial (−)
Refractive index	n = 1.479–1.493
Pleochroism	None
Ultraviolet fluorescence	Short UV = Greenish blueish white Long UV = Green, creamy white-yellow
Fusibility	3.5
Other characteristics	Weakly piezoelectric and pyroelectric; weakly electrostatic when rubbed or heated

Analcime (/əˈnælsiːm, -saɪm/; from Ancient Greek ἀνάλκιμος (análkimos) 'not strong') or analcite 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.^[1] Analcime is not classified as an isometric crystal, as although the crystal structure appears to be isometric, it is usually off only by a fraction of an angle. However, there are truly isometric samples of the mineral, which makes its classification even more difficult.^[2] Due to the differences between the samples being too slight, there's no merit from having multiple species names, so as a result analcime is a common example for minerals occurring in multiple crystal systems and space groups. It was first described by French geologist Déodat de Dolomieu, who called it zéolithe dure, meaning hard zeolite. It was found in lava in Cyclops, Italy. The mineral is IMA approved, and had been grandfathered, meaning the name analcime is believed to refer to a valid species til this day.^[3]