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Rocks

Rocks. Mineral mixtures. What are rocks?. All natural rocks are aggregates of minerals The formation of rocks and their physical properties are linked. How and where do rocks form?. Many rocks originate from observable processes that take place at the Earth’s surface.

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Rocks

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  1. Rocks Mineral mixtures

  2. What are rocks? • All natural rocks are aggregates of minerals • The formation of rocks and their physical properties are linked

  3. How and where do rocks form? • Many rocks originate from observable processes that take place at the Earth’s surface. • Rocks that do not appear to be like surface rocks give us clues to processes active within the Earth.

  4. Rock Classification • Rocks are classified according to the processes that form them. • Formed by the solidification of magma • The breakdown of pre-existing rock • Solid state transformation of minerals in a pre-existing rock.

  5. Three types of Rocks • Based on the processes of formation three main categories of rocks are recognized: • Igneous • Sedimentary • Metamorphic

  6. Igneous Rocks • Crystallized material from molten magma. • Volcanic processes = volcanic rocks • “Beneath the crust” processes = plutonic rocks • Volcanic Rocks = extrusive • Plutonic Rocks = intrusive

  7. Cooling of Magma • Rapid cooling of magma (extrusive) normally produces rocks with small mineral grains • Slow cooling of magma (intrusive) normally produces rocks with large mineral grains

  8. Sedimentary Rocks • Deposition and precipitation of materials from the breakdown of older rocks • Occurs on Earth’s surface • Weathering can be: • Chemical – materials dissolve in water • Physical – broken fragments (clasts)

  9. Deposition vs. Precipitation • Clastic sediments can be lithified (cemented together) to form clastic sedimentary rocks • Fragments are cemented with precipitates or simply by compaction • Materials dissolved in water will precipitate when conditions are right to form chemical sedimentary rocks

  10. Bedding • Sedimentary rocks are recognized by distinctive bedding or layering • Bedding is a key feature in recognizing paleo-environments

  11. Metamorphic Rocks • Either sedimentary or igneous rocks are transformed by processes occurring within the Earth’s crust. • Increased pressure • Increased temperature • Chemical reactions catalyzed by hot fluids (water most often)

  12. http://www.beavton.k12.or.us/greenway/leahy/00-01/rocks/gneiss.jpghttp://www.beavton.k12.or.us/greenway/leahy/00-01/rocks/gneiss.jpg Types of Metamorphic Rocks • Regional Metamorphism • Affecting vast areas • Often at plate boundaries • Contact Metamorphism • Very localized • Occurs adjacent to volcanic or plutonic activity

  13. 3. Hydrothermal Metamorphism • Hot water flows through the rocks causing a chemical reaction and thus modifying the properties • Often causes the precipitation of metal-ore deposits

  14. Minerals found in metamorphic rock depend on the minerals found in the parent rock. And the nature of the metamorphic processes. • Similarities in appearance to sedimentary rocks and igneous rocks • Bedding and banding at first glace look the same • Mineral assemblage appears similar to igneous – generally has more silicates

  15. The Rock Cycle

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