| First-order categories: | |
| F | Fresh lavas near seafloor |
| O | Opal-bearing altered rocks |
| X | Cristobalite-bearing altered rocks |
| Y | Quartz-bearing altered rocks |
| Z | Altered rocks lacking silica phases, generally occurring as fragments in hydrothermal breccias or between stockwork quartz veins |
| A | Albite-rich altered rocks (andesite precursors) |
| U | Unclassified |
| Second-order categories: | |
| M | Plagioclase (mostly microlites) retained |
| B | Pyrophyllite-bearing "bleached" rocks |
| Third-order categories: | |
| -K | Kernels in samples with fracture-controlled pale selvages |
| -T | Transition zones between kernels and selvages |
| -S | Pale selvages |