|
| Composition | SiO2 • nH2O |
| | Optic class & sign | Isotropic |
| | Relief | Mod-negative |
| | Refractive Index | 1.435 -1.460
|
|
| n decreases with increasing H2O content |
| | Birefringence | Isotropic; may have weak anomalous birefringence |
| | Colour | Colourless; ranges of pale colours possible |
| | Zoning | |
|
|
| Alteration / decomposition | Tends to convert to quartz |
|
|
| Occurence | Ign | |
| | | Met | |
| | | Sed | Accumulation of siliceous microfossils; surface or near-surface silica precipitates from meteoric water; cement in some sandstones |
| | | Hyd | |
| | | Other | |
|
|
| Distinctive properties | Moderate-negative relief, isotropy, form, occurrence |
| | Additional comments | Water content ca. 2 to 10 wt.% |
|
|
Images 