Gmelinite
| Gmelinite | |
|---|---|
| General | |
| Category | Tectosilicate minerals |
| Group | Zeolite group |
| Formula | Na4(Si8Al4)O24·11H2O |
| IMA symbol | Gmelinite-Na: Gme-Na |
| Strunz classification | 9.GD.05 (10 ed) 8/J.26-50 (8 ed) |
| Dana classification | 77.1.2.6 |
| Crystal system | Hexagonal |
| Crystal class | Dihexagonal dipyramidal (6mmm) H-M symbol: (6/m 2/m 2/m) |
| Space group | P63/mmc |
| Unit cell | a = 13.78, c = 10.03 [Å]; Z = 4 |
| Identification | |
| Formula mass | 2,000.77 g |
| Color | Colorless, white, yellow, orange, pale green, pink, red, brown and grey |
| Crystal habit | Hexagonal plates, or short prisms, showing hexagonal dipyramids, pyramids and basal pinacoid. {1010}, {1011} and {0001} dominant. May also be tabular or rhombohedral. Crystals are striated parallel to (0001) |
| Twinning | Interpenetrant twins common on {1011}. The twins consist of four individuals, three are at 90° to the other and at 60° to each other |
| Cleavage | Good on {1010} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 4+1⁄2 |
| Luster | Dull to vitreous |
| Streak | White |
| Diaphaneity | Transparent, translucent or opaque |
| Specific gravity | 2.04 to 2.17 |
| Optical properties | Uniaxial (-) |
| Refractive index | nω = 1.476 - 1.494, nε = 1.474 - 1.480 |
| Birefringence | δ = 0.002 - 0.014 |
| Solubility | Soluble in cold 10% HCl. |
| Other characteristics | Piezoelectric. Barely detectable radioactivity. As with all zeolites, water is released on heating, and almost all has been expelled by 400 °C. |
| References | |
Gmelinite is a series of rare zeolite minerals. The most common member is gmelinite-Na; others are gmelinite-Ca and gmelinite-K. It is closely related to the very similar mineral chabazite. Gmelinite was named as a single species in 1825 after Christian Gottlob Gmelin (1792–1860) professor of chemistry and mineralogist from Tübingen, Germany, and in 1997 it was raised to the status of a series.
Gmelinite-Na has been synthesised from Na-bearing aluminosilicate gels. The naturally occurring mineral forms striking crystals, shallow, six sided double pyramids, which can be colorless, white, pale yellow, greenish, orange, pink, and red. They have been compared to an angular flying saucer.