1. 3.2 Igneous Rocks Igneous comes from the Latin word which means “fire” Igneous rocks form by “crystallization” when hot molten rock solidifies.

2. Classifications: A. Intrusive Rocks (Plutonic Rock) 1. Rocks that form when magma hardens beneath Earth’s surface. 2. Cools slowly, forms large crystals. Example: granite

3. A.Extrusive Rocks (Volcanic Rock) 1.Rocks that form when lava hardens at Earth’s surface 2.Cools rapidly, forms small crystals. Example: rhyolite

4. 3.2 Igneous Rocks When Magma/Lava composition is mainly: quartz & feldspar (Si and O) then they are considered “Felsic.” They tend to be light in color and with a low specific gravity. (sometimes called granitic composition)

5. 3.2 Igneous Rocks When Magma/Lava composition is mainly olivine or pyroxine (Mg, Fe) then they are considered “Mafic.” They tend to be dark in color and with a high specific gravity. (sometimes called basaltic composition)

6. Formation of Igneous Rocks 1. F fire 2. C intrusive igneous (plutonic) 3. G extrusive igneous (volcanic) 4. A magma 5. D lava 6. B granite 7. E rhyolite

7. Composition is the same, mostly quartz, feldspar and hornblend. Texture is very different

8. Compare/Contrast Igneous Rocks GraniteRhyolite Compare Igneous, composition- quartz, feldspar, hornblend (felsic) Igneous, made of quartz, feldspar, (felsic) Contrast Slow cooling from magma Intrusive/Plutonic Large crystals Rapid cooling from lava Extrusive/Volcanic Small crystals

9. Igneous Rock Classification 9. Texture and composition Texture – size, shape and arrangement of interlocking crystals Composition – proportions of light and dark minerals in the rock

10. Classification Terminology Large Crystals / Coarse Grained Small Crystals / Fine Grained GlassyPorphyritic Very slow cooling Large crystals Rapid cooling Small interconnected crystals Very fast cooling No crystal s Different sized crystals Crystals did not form at same rate

11. Composition Terminology Felsic/ Granitic Mafic/ Basaltic Other Light colored silicate minerals Quartz/ feldspar Dark colored silicate minerals Fe, Mg, plagioclase feldspar Andesitic – Ultramafic- andesite lava peridotite Rock olivine & 25% dark pyroxene Silicate and not found plagioclase at Earth’s Feldspar surface

12. Classification of Igneous Rocks 10. True 11. Mafic composition ( basaltic) 12. a, b, c, d 13. Ultramafic 14. False 15. b