Table 1. Summary of clay-size mineral groups.
| Groups | Major clay-size minerals | Structure* |
|---|---|---|
| Gibbsite | gibbsite | 1 (octahedral) |
| Kaolinite | kaolinite, halloysite | 1:1 |
| Illite/mica | illite, mica | 2:1 |
| Smectite | montmorillonite | 2:1 |
| Vermiculite | vermiculite | 2:1 |
| Chlorite | chlorite | 2:1:1 |
| Iron (Fe) oxide | goethite, hematite | mixed |
| Quartz | quartz | crystal |
| Non-crystalline | allophane, imogolite, ferrihydrite | amorphous |
| Others | feldspar, etc. | mixed |
*Silicate layer or other structural characteristics of clay-size minerals. Numbers indicate the numbers of tetrahedral: octahedral (: inter-layer) sheets.