| Other names: | Moss opal or moss agate (with manganese oxide deposits) |
| Mineral class: | Silicate |
| Composition: | Hydrated silica, SiO2 nH2O |
| Hardness: | 5 - 6 |
| Color: | White, yellow, brown, red, grey, blue, transparent |
| Crystal form: | Seemingly noncrystalline; deposited as a jellylike substance that later hardens. |
| Environment: | Petrifying material in much fossil wood. Deposited by hot springs. |
| Comments: | Scratched by quartz but not by penny; may or may not be scratched by knife. Unhydrated silica is quartz, which is slightly harder. |