Analcime

Analcime
Reddish crystals of analcime up to 1.8 cm in size on matrix
General
CategoryZeolite
Formula
(repeating unit)
NaAlSi2O6 · H2O
IMA symbolAnl
Strunz classification9.GB.05
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupIbca
Identification
Formula mass220.15
ColorWhite, colorless, gray, pink, greenish, yellowish
Crystal habitTypically in crystals, usually trapezohedrons, also massive to granular.
TwinningPolysynthetic on [001], [110]
CleavageIndistinct on {001}, {010}, {100}
FractureUneven to subconchoidal
Mohs scale hardness5–5.5
LusterVitreous
StreakWhite
DiaphaneityTransparent to subtransparent to translucent
Specific gravity2.24–2.29
Optical propertiesIsotropic; anomalously biaxial (−)
Refractive indexn = 1.479–1.493
PleochroismNone
Ultraviolet fluorescenceShort UV = Greenish blueish white
Long UV = Green, creamy white-yellow
Fusibility3.5
Other characteristicsWeakly piezoelectric and pyroelectric; weakly electrostatic when rubbed or heated

Analcime (/əˈnælsm, -sm/; 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]

  1. ^ Cite error: The named reference :1 was invoked but never defined (see the help page).
  2. ^ "Analcime (analcite): The zeolite mineral analcime information and pict". www.minerals.net. Retrieved 2022-12-29.
  3. ^ "Analcime". www.mindat.org. Retrieved 2022-12-29.