Last modified 10 / 07
| Metallic | H<2.5 | H 2.5 to 3.5 | H 3.5 to 5.5 | H >5.5 | Glossary | Tests | Index |
| Rock Summary | Igneous | Sedimentary | Metamorphic |
|
|
Felsic |
Intermediate |
Mafic |
Ultramafic |
|
Fine Grain |
Rhyolite |
Andesite |
Basalt |
Conditions needed for ultramafic eruptions have been extremely rare through geologic time. |
|
Intermediate |
--- |
Dacite |
Diabase |
--- |
|
Coarse Grain |
Granite |
Diorite |
Gabbro |
Peridotite |
|
Glassy |
Obsidian |
--- |
--- |
--- |
|
Frothy |
Pumice |
--- |
Scoria |
--- |
It is important to note that there are many, many intermediate steps between these main divisions. Geology is a science full of "shades of gray," and the naming of igneous rocks is certainly no exception. Therefore, names like "grano-diorite," "andesitic-basalt," and "rhyo-dacite porphyry" are perfectly acceptable.
| Metallic | H<2.5 | H 2.5 to 3.5 | H 3.5 to 5.5 | H >5.5 | Glossary | Tests | Index |
| Rock Summary | Igneous | Sedimentary | Metamorphic |
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