Igneous Rock Key
| Crystal Size | Composition | Rock |
|---|---|---|
| Phaneritic | Ultramafic | Peridotite |
| Mafic | Gabbro | |
| Intermediate | Diorite | |
| Felsic | Granite |
| Crystal Size | Composition | Rock |
|---|---|---|
| Aphanitic | Mafic | Basalt |
| Intermediate | Andesite | |
| Felsic | Rhyolite |
| Crystal Size | Composition | Rock |
|---|---|---|
| Porphyritic | Mafic | Basalt Porphyry |
| Intermediate | Andesite Porphyry | |
| Felsic | Rhyolite Porphyry |
| Texture | Color | Rock |
|---|---|---|
| Glassy | Black, brown, red | Obsidian |
| Vesicular (containing a great number of bubble holes formed by escaping gas) |
Dark; heavy | Vesicular Basalt |
| Dark; light weight | Scoria | |
| Light | Pumice | |
| Pyroclastic (ash and broken pieces of lava and glass formed into rock) |
Any color | Tuff or Breccia |