Volcanic Rocks
The book uses lots of names for volcanic rocks and other igneous rocks that can get confusing.
Volcanic (extrusive) rocks are classified in almost exactly the same way as plutonic (deep intrusive) rocks. The principal difference is that volcanic rock names are substituted for their plutonic equivalents:
| Plutonic Rock | Volcanic Equivalent |
| Granite | Rhyolite |
| Granodiorite | Dacite |
| Tonalite | Quartz Andesite |
| Syenite | Trachyte |
| Monzonite | Latite |
| Diorite | Andesite |
| Gabbro | Basalt |
| Monzogabbro (or diorite) | Latite-basalt (or andesite) |
This diagram below show how the different kinds of igenous rock can be distinguished by their chemistry using a “simple” plot of Silicon against the total amount of Potassium and Sodium.
