Erionite
| Erionite | |
|---|---|
| General | |
| Category | Tectosilicate minerals |
| Group | Zeolite group |
| Formula | (Na 2,K 2,Ca) 2Al 4Si 14O 36•15H 2O |
| IMA symbol | Eri |
| Crystal system | Hexagonal |
| Crystal class | Dihexagonal dipyramidal (6mmm) H-M symbol: (6/m 2/m 2/m) |
| Space group | P63/mmc (no. 194) |
| Identification | |
| Color | White, Green, Gray, Orange |
| Crystal habit | Acicular - Occurs as needle-like crystals (asbestosform). |
| Cleavage | [010] Distinct |
| Fracture | Splintery |
| Mohs scale hardness | 3.5-4 |
| Luster | Vitreous - silky |
| Streak | white |
| Specific gravity | 2.09 - 2.13 avg = 2.11 |
| Optical properties | Uniaxial (-) |
| Refractive index | nω = 1.4711, nε = 1.474 |
| Birefringence | δ = 0.0191 |
| Other characteristics | non-magnetic, non-radioactive, toxic if inhaled |
| References | |
Erionite is a naturally occurring asbestiform mineral that belongs to a group of minerals called zeolites. It usually is found in volcanic ash that has been altered by weathering and ground water. Erionite forms brittle, wool-like fibrous masses in the hollows of rock formations and has an internal molecular structure similar to chabazite. This mineral is likely as toxic as asbestos; however, erionite is not currently regulated by the U.S. Environmental Protection Agency and there are no occupational exposure limits for erionite fibers. Erionite was first described by A.S. Eakle in 1898, as white woolly fibrous masses in cavities in rhyolite lava near Durkee, Oregon. It was originally thought to be another relatively rare zeolite named offretite, which is very similar to erionite in appearance and chemical composition.