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Rocks

Rocks. The Rock Cycle. Magma—molten material that forms inside the Earth It crystallizes either beneath the surface or as a result of volcanic activity to make Igneous Rock It weathers, is transported, and deposited to become Sediment

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Rocks

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  1. Rocks

  2. The Rock Cycle • Magma—molten material that forms inside the Earth • It crystallizes either beneath the surface or as a result of volcanic activity to make • Igneous Rock • It weathers, is transported, and deposited to become • Sediment • It goes through lithification (changes into rock) to become

  3. The Rock Cycle • Sedimentary Rock • If it is exposed to great heat and pressure because of mountain building or being intruded with magma, it will change into • Metamorphic Rock • If it is exposed to more heat and/or pressure, it will melt and become • Magma

  4. The Rock Cycle • The full cycle does not always take place due to “shortcuts” or interruptions

  5. The Rock Cycle

  6. Igneous Rock • “Formed by Fire” • Slow cooling results in the formation of large crystals • Rapid cooling results in the formation of very small microscopic crystals

  7. Classifying Igneous Rock • Texture—Size and arrangement of the interlocking crystals • Fine-grained—microscopic crystals • Example: rhyolite • Course-grained—able to be seen unaided • Example: granite • Porphyritic—large crystals embedded in a matrix of smaller crystals • Example: andesite porphyry • Glassy—rapid cooling of molten rock ejected into the atmosphere during a volcanic eruption • Examples: obsidian, pumice

  8. Classifying Igneous Rock • Mineral Composition • Depends on the chemical composition of the magma from which it crystallizes • Influenced by crystal settling in the magma (density of the components)

  9. Naming Igneous Rocks • Basaltic Rocks • Derived from the first minerals to crystallize • Rich in iron and magnesium • Example: basalt • Granitic rocks • From the last minerals to crystallize • Mainly feldspar and quartz • High silica content • Example: granite

  10. Naming Igneous Rock • Rocks may have the same compositions, but are named differently because of their different textures.

  11. Sedimentary Rocks • Compacted and cemented sediment • Geologists date the Earth based on layers of sediment • Sediment can contain fossils • Economically important • Coal, natural gas, oil • Iron, aluminum, manganese, fertilizer, sand and gravel

  12. Classifying Sedimentary Rocks • Detrital • Form from solid particles from weathered rocks • Classified by particle size • Examples: • Shale (most abundant) • Sandstone • Conglomerate • Siltstone

  13. Classifying Sedimentary Rocks • Chemical • From material that was once in solution and precipitates to form sediment • Common Rocks: • Limestone (most abundant) • Travertine • Microcrystalline quartz • Chert, flint, jasper, agate • Evaporites • Rock salt, gypsum • Coal • Lignite, bituminous

  14. Lithification of Sedimentary Rocks • Compaction • Weight of overlying material compresses deeper sediments • Cementation • Materials such as calcite, silica, and iron oxide are carried in solution by water moving through the pore spaces between particles

  15. Features of Sedimentary Rocks • Strata or beds—layers of accumulated sediment • Bedding planes—flat surfaces along which rocks tend to separate or break • Fossils

  16. Metamorphic Rocks • Changed in Form • From heat, pressure, and chemically active fluids • Takes place when rock is subjected to conditions unlike those in which it originally formed • Regional metamorphism (mountain building) and contact metamorphism (molten material bake surrounding rock)

  17. Three Metamorphic Agents • Heat • Most important agent of metamorphism • Provides energy to drive chemical reactions that rearrange crystal structures • Increases with depth

  18. Three Metamorphic Agents • Pressure • Increases with depth • Stress during mountain building • Rock at great depth is warm and becomes plastic-like during deformation

  19. Three Metamorphic Agents • Chemically active fluids • Water is contained in pore spaces of virtually every rock • It acts as a catalyst to help ions migrate to form crystalline shapes

  20. Metamorphism Changes Texture • Foliated • Some minerals under pressure will recrystallize in an alignment that looks layered • Examples: • Shale becomes slate • Shists—metamorphic rocks that are platy • Gneiss—metamorphic rocks that are elongated and granular

  21. Metamorphism Changes Texture • Nonfoliated • Some metamorphic rocks are composed of only one mineral • Examples: • Limestone becomes marble • Quartz sandstone can become quartzite

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