Table T8. Classification of volcanic basement lithologies. (See table note.)
| Phenocryst abundance |
| Aphanitic rocks: |
| Aphyric: <1% |
| Sparsely phyric: 1%–2% |
| Moderately phyric: 2%–10% |
| Highly phyric: >10% |
| Degree of crystallinity |
| Holohyaline: 100% glass |
| Hypohyaline: ≥50% glass |
| Hypocrystalline: ≥50% crystals |
| Holocrystalline: 100% crystals |
| Grain size |
| Aphanitic rocks: |
| Cryptocrystalline: very fine crystals visible, but not identifiable with a petrographic microscope |
| Microcrystalline: small crystals (≤0.01 mm) identifiable with a petrographic microscope |
| Microlitic: partially crystalline rock containing small euhedral crystals, identifiable with a petrographic microscope |
| Phaneritic rocks*: |
| Fine grained: <1 mm |
| Medium grained: 1–5 mm |
| Coarse grained: >5 mm |
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