Nepheline
Nepheline, also called nephelite (from Ancient Greek νεφέλη (nephélē) 'cloud'), is a rock-forming mineral in the feldspathoid group – a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. It is used in glass and ceramic manufacturing and other industries, and has been investigated as an ore of aluminium.
| Nepheline | |
|---|---|
| General | |
| Category | Tectosilicate, feldspathoid |
| Formula (repeating unit) | (Na,K)AlSiO4 |
| IMA symbol | Nph |
| Strunz classification | 9.FA.05 |
| Crystal system | Hexagonal |
| Crystal class | Pyramidal (6) H–M symbol: (6) |
| Space group | P63 |
| Identification | |
| Formula mass | 146.08 g/mol |
| Color | White, gray, brown, brownish gray, or reddish white |
| Crystal habit | Massive granular to prismatic |
| Twinning | On [1010], [3365], and [1122] |
| Cleavage | [1010] Poor |
| Fracture | Subconchoidal |
| Mohs scale hardness | 6 |
| Luster | Vitreous to greasy |
| Streak | White |
| Specific gravity | 2.55–2.65 (average: 2.59) |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.529–1.546 nε = 1.526–1.542 |
| Birefringence | δ = 0.003–0.004 |
| Other characteristics | non-radioactive, non-magnetic, non-fluorescent |
| References | |
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