4.5 Putting It All Together: Igneous Rock Identification
Identifying Igneous Rocks
Texture, chemical composition, color, mineralogy–these are all you need to identify most of the igneous rocks out there! Let’s put your identification skills to the test by assigning names to each of the rock samples! To help you make your final determinations, consult this short guide on each of the 10 igneous rocks:
- Granite – Felsic, coarse-grained, light-colored
- Rhyolite – Felsic, fine-grained, light-colored
- Diorite – Intermediate, coarse-grained, black/dark gray minerals in a light matrix “cookies and cream”
- Andesite – Intermediate, fine-grained, gray to tan with fine black grains “salt and pepper”
- Gabbro – Mafic, coarse-grained, dark-colored
- Basalt – Mafic, fine-grained, dark-colored
- Scoria – Mafic, porous, dark-colored, less dense than most rocks, but does not float in water
- Pumice – Felsic, porous, light-colored, very low density/can often float in water
- Tuff — Felsic to intermediate, light-colored, pyroclastic texture, can sometimes see glass in matrix
- Obsidian —Felsic, but dark-colored, glassy texture with a conchoidal fracture
In this section, you will view a short video of each rock, and then, based on the characteristics you can observe, you will identify the rock by its proper name.
