Igneous rocks are classified based on their texture and mineral composition. Texture is determined by whether the rock solidified underground from slowly cooling magma (intrusive/coarse-grained) or above ground from quickly cooling lava (extrusive/fine-grained). Composition depends on the minerals present, with light-colored felsic rocks like granite having high silica and dark mafic rocks like basalt having low silica. Some igneous rocks like obsidian, pumice, and scoria have additional distinguishing features.

1. Igneous Rocks Are grouped by mineral composition and texture

2. 1. Texture Size and arrangement of mineral crystals igneous crystals often interlocking

3. A. Intrusive Texture Intrusive: formed underground from magma that cooled SLOWLY large, easily seen crystals

4. Intrusive- coarse- plutonic

5. Igneous rocks w/ large crystals are known as: Intrusive= plutonic= coarse-grained ex: granite

6. Granite

7. Intrusive-Plutonic-Coarse Grained Granite

8. B. Extrusive Texture Extrusive: formed above ground from lava that cooled QUICKLY small crystals, often hard to see

9. Igneous rocks w/ small crystals are known as: extrusive= volcanic= fine-grained ex: basalt, rhyolite Rhyolite : Extrusive Fine Grained Volcanic

10. Basalt: Extrusive Fine Grained Volcanic

11. 2. Composition Is the mineral content often shown as color of rock

12. A. Felsic Felsic rocks are light colored have hi silica content most intrusive rox are felsic

13. felsic Granite Rhyolite

14. B. Mafic Mafic rocks are: dark colored low in silica most extrusive rocks are mafic ex: basalt

15. Basalt

16. Some igneous rocks are hard to classify: Obsidian: glassy

17. Porphyritic: full of holes porphyritic

18. pumice: full of holes; floats scoria: full of holes; doesn’t float

19. Floating Pumice

20. Scoria

22. Click on Picture Below for Animation and Go Through Each Page. Answer the Questions as You Go.