1. Igneous Rocks

2. Rock vs. Mineral Rock- a naturally formed consolidated material composed of grains of one or more minerals. Mineral- a naturally occurring element or compound with a relatively constant chemical and structural composition.

3. Three Rock Types 1.Igneous: Rock formed from the cooling of magma 2.Sedimentary: Rock formed from the accumulation and lithification (cementing) of weathered material. 3.Metamorphic: Rocks formed by the altering existing rock by heat and/or pressure.

4. The Rock Cycle

5. How do igneous rocks form? Intrusive Extrusive

6. Identification of Igneous Rocks Texture : the size of the grains that make up the rock Mineralogy : the minerals present in the rock

7. Textures: Phaneritic (Fan-er-itic): all large grainsAphanitic (A-fan-itic): all small grains Porphyritic (Poor-for-itic): large crystals surrounded by fine-grained matrix

8. Terms to explain to chemistry of igneous rocks: Mafic: (May-fik) Silica deficient igneous rocks with a high content of Magnesium, Iron, and Calcium. More dark minerals than light minerals. Felsic: (fell-sick) Silica rich igneous rock with a high percentage of potassium and sodium. Usually lots of quartz and feldspar.

9. Mineral content of Igneous Rocks

10. Intrusive Structures: Rock formations caused by the cooling of magma beneath the Earth’s Surface.

11. Shiprock, New Mexico Formed when a volcano goes extinct (loses its heat source). The magma that was inside the volcano cools and hardens into a rock much harder than that on the surface. Eventually the volcano is weathered away, exposing the rock.

12. Devil’s Tower, WY

13. Dikes: Magma from below is pushed up into cracks in the existing rock.

14. Dikes from Intrusion

15. Magma Formation molten rock created near the subduction zone. granitic magma ~ 650 o C geothermal gradient – 3 o C/100 m melting point increases with pressure; pressure increases with depth. mineral melting point is lowered by water under pressure.

16. Bowen’s Reaction Series sequence in which minerals crystallize in cooling magma.

17. Volcanism and Extrusive Rocks pyroclastic (pyro = “fire”; clast = “broken”) pyroclastic flow- mixture of gas and pyroclastic debris. caldera- pumice- vesicles- cinder cone-

18. Extrusive Rocks pyroclastic flow (click the picture below for a short video pumice with vesicles

19. Pyroclastic Flows

20. volcanos cinder conecaldera