Rock Identification

1. Igneous, Sedimentary, and Metamorphic Rocks Rock Identification

2. The Rock Cycle

3. Igneous Rocks • Solidified products of once-molten material called magma • Interlocking arrangement of mineral crystals that forms as the molten material cools and crystals grow • Intrusive: form below the Earth’s surface • Extrusive: formed at the Earth’s surface

4. Identifying Igneous Rocks • The rate of cooling determines the size of the interlocking crystals. • Slower cooling = Larger crystals • Igneous rocks are identified based on texture.

5. Igneous Textures • Coarse Grained- Majority of crystals are of a uniform size and can be seen without magnification. • Fine Grained- Very small crystals which are generally not identifiable without magnification.

6. Igneous Textures • Polyphyritic- Two very contrasting sizes of crystals caused by magma cooling at two different rates. • Glassy- No mineral crystals develop because of very rapid cooling.

7. Igneous Textures • Fragmented- The rock contains broken, angular fragments of rocky material produced during an explosive volcanic eruption.

8. Sedimentary Rocks • Form at or near Earth’s surface from the accumulated products of weathering (sediments) • Lithification transforms the sediment into hard rock • Can be classified as either detrital rocks or chemical rocks

9. Detritral Sedimentary Rocks • Detrital- consists mineral grains or rock fragments derived form the process of mechanical weathering. Identification is based on the size of grain.

10. Chemical Sedimentary Rocks • Chemical- previously dissolved in water and later precipitated by either inorganic or organic processes. Mineral composition is used to identify.

11. Metamorphic Rocks • Forms below Earth’s surface with high temperatures and pressures. • Rocks are identified by both texture and composition.