1. These notes go on pp. 7 & 9 of your Igneous rock INB!!!

2. Igneous rocks are formed by the crystallization of molten rock (lava or magma).

3. Classification 1.Mineral Composition 2.Texture of Grain Size

4. Mineral Composition

5. Felsic: high amounts of silica & light in color

6. Felsic Rocks and Minerals

7. Mafic: low amounts of silica & dark in color

8. Mafic Rocks

9. Silica Composition Felsic rocks - more than 65% silica content Intermediate rocks - 50-65% silica content (also called andesitic) Mafic rocks - less than 40-50% silica

10. Pure Silica

11. Texture of Grain Size

12. Texture of grains in igneous rocks depends on where the rock forms. Where it forms, will change the rate of cooling.

13. 1. Igneous rocks formed above ground from lava are called “Extrusive” or “Volcanic” rocks. Obsidian Rhyolite

14. cools rapidly and crystals have a limited time to form; as a result there are small or no mineral crystals

15. Resulting Textures: 1.Glassy 2.Porous/Vesicular 3.Fine-Grained

16. Obsidian-Glassy Felsic

17. Scoria-Vesicular Mafic

18. 2. Igneous rocks formed underground from Magma are called Plutonic or Intrusive rocks. Notice the large crystals

19. cools slowly and large crystals have time to form.

20. Resulting Textures 1. Coarse Grained

21. Granite- Coarse-grained Felsic

22. Gabbro- Coarse-grained Mafic

23. Igneous rocks that begin to cool underground and then are erupted to the surface have both fine and coarse grains. These rocks have undergone two stages of cooling, therefore they have two sizes of crystals. These rocks have porphyritic texture.

24. Basalt Porphyry- Mafic

25. Rhyolite Porphyry-Felsic

26. These notes go on p. 9 of your INB!!!

27. Intrusive Igneous Rock formations:

28. Dikes Dike: Sheet-like Igneous rocks that cut across the structure of pre-existing rock.

29. Dike

30. Sills Sills: Sheet-like Igneous rock that lies parallel to the layering of pre-existing rock.

31. Sill

32. Laccoliths Laccoliths: vertically developed sills.

33. Batholiths Batholiths: a large Plutonic mass of Igneous Rock. Usually makes up the core of volcanic mountains

36. Halfdome- Yosemite, California

37. Enchanted Rock-Texas