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Physical Geology

Physical Geology. Chapter 6. Part 1. The Rock Cycle. Rocks are solid pieces of the earth of any size. They can be made up of one or more minerals, or they can be made up of solid organic matter. 3 Types by Origin. Igneous – “from fire”; forms by cooling of magma or lava

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Physical Geology

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  1. Physical Geology Chapter 6

  2. Part 1 The Rock Cycle

  3. Rocks are solid pieces of the earth of any size. They can be made up of one or more minerals, or they can be made up of solid organic matter.

  4. 3 Types by Origin • Igneous – “from fire”; forms by cooling of magma or lava • Sedimentary – formed from compaction and cementation of rock fragments (sediments) • Metamorphic – “changed form”; from alteration of existing rock by heat, pressure and time

  5. Rock Cycle

  6. Igneous may become sedimentary, metamorphic, or igneous • Sedimentary may become metamorphic, igneous, or sedimentary • Metamorphic may become igneous, sedimentary, or metamorphic

  7. Rock Properties • Bowen’s Reaction Series – As magma cools, certain minerals tend to crystallize first. As they form out, they remove certain elements from the magma, which changes the composition of it. Thus different minerals form at different times during the cooling and solidification, and they generally always form in the same order.

  8. The Canadian geologist N.L. Bowen found that minerals tend to form in specific sequences in igneous rocks, and these sequences could be assembled into a composite sequence.

  9. In Summary

  10. Chemical Stability • Tendency to maintain original chemical composition • Based on strength of chemical bonds • Highest # of bonds between Si and O are most resistant

  11. Physical Stability • Reduced by zones of weakness • Layer joints • Joints between crystalline formations • Joints and fractures from release of formative pressures

  12. Part 2 Igneous Rock

  13. Magma is melted rock below the surface; liquid or fluid • Melting depends upon • Temperature • Pressure • Presence of fluids • Melt temperature depends upon the chemical composition of the rock • Pressure heightens melting point; release lowers • Fluids decrease some melting points

  14. Partial Melting • Different components have different melting points • As each melts, magma composition of the magma is altered • Opposite effect of Bowens Series

  15. Fractional Crystallization • Opposite of partial melting • Minerals crystallize and change makeup of magma chemically • In same order as Bowens Series • Longer formation time = larger crystals • Shorter time = smaller crystals • Inner/outer crystals may be different due to differences in the magma as time goes by

  16. Igneous Rock Textures • Coarse grained – slow loss of heat by subsurface magma results in large, well-developed crystals (rough granite)

  17. Igneous Rock Textures • Fine grained – rapid heat loss from superficial lava results in small, poorly developed crystals (smooth basalt)

  18. Igneous Rock Textures • Porphyritic – magma cools somewhat slowly, then speeds up near or on surface resulting in a mixed appearance/texture

  19. Igneous Rock Textures • Glassy – viscous magma cools quickly with few dissolved gases forming few, if any crystals Obsidian

  20. Igneous Rock Textures • Vesicular - viscous magma cools quickly with a lot of dissolved gases forming few, if any crystals, but many bubbles (vesicles) Pumice

  21. Igneous Rock Composition • Felsic – lots of silica; light color; has minerals feldspar, mica and quartz; e.g., granite, rhyolite, obsidian, pumice • Mafic – rich in Fe and Mg; dark color; minerals pl feldspar, pyroxene, ferromagnesians (hornblende); e.g., basalt and gabbro • Intermediate – intermediate silica content;plagioclase, hornblende,pyroxene, and biotite; e.g., diorite and andesite

  22. Igneous Rock Composition • Felsic – lots of feldspar (fel); lots of silica (sic) • Mafic – rich in Fe (f) and Mg (Ma) or ferromagnesians • Intermediate – intermediate blend

  23. Intrusive formations batholith

  24. Extrusive formations

  25. Some uses of Igneous rock: GRANITE: An igneous-plutonic rock, medium to coarse-grained that is high in silica, potassium, sodium and quartz but low in calcium, iron and magnesium. It is widely used for architectural construction, ornamental stone and monuments. PUMICE: An igneous-volcanic rock, it is a porous, brittle variety of rhyolite and is light enough to float. It is formed when magma of granite composition erupts at the earth’s surface or intrudes the crust at shallow depths. It is used as an abrasive material in hand soaps, emery boards, etc. GABBRO: An igneous-plutonic rock, generally massive, but may exhibit a layered structure produced by successive layers of different mineral composition. It is widely used as crushed stone for concrete aggregate, road metal, railroad ballast, etc. Smaller quantities are cut and polished for dimension stone (called black granite). BASALT: An igneous volcanic rock, dark gray to black, it is the volcanic equivalent of plutonic gabbro and is rich in ferromagnesian minerals. Basalt can be used in aggregate.

  26. Practice questions for igneous rocks

  27. Part 3 Sedimentary Rock

  28. Beginnings - sediments

  29. ……then…..

  30. Lithification in this case means compaction (squeezed together tightly reducing pore space) and cementation (glued together by chemicals in the water) of the sediments into rock

  31. Classes by origin • Chemical • Organic • Clastic

  32. Chemical • Dissolved minerals • Precipitate to layers as evaporites or chemical reaction products • Examples: halite, gypsum Bonneville Salt Flats, Utah

  33. Organic • Remains of living things • Heavy deposits • Examples: coal, chalk and organic limestone

  34. Clastic • Imported fragments that are lithified • By fragment size • Conglomerate (breccia) – large fragments cemented by small • Sandstone – quartz fragments (sand) • Shale – clay sized fragments usually compacted into flat layers

  35. ClastIc

  36. Characteristics of Clastic Sediments • Sorting – tendency of currents to separate sediments according to size • Angularity – collisions during movement of particles tends to round them off. Little movement = angular; more movement = more rounded/smooth; great movement = most rounded/smooth particles

  37. AngularityPatterns

  38. Sedimentary Rock Features • Stratification • Cross bedding • Graded bedding • Ripple marks • Mud cracks • Fossils • Concretions

  39. Stratification – in layers or beds

  40. Cross beds – slanting layers

  41. Graded beds – bed of sediments assorted by size

  42. Ripple marks & Mud cracks

  43. Fossils

  44. Concretions and geodes

  45. Sedimentary rocks have great economic importance - • Oil, natural gas, coal, and uranium, our major energy resources, are formed in and come from sedimentary rocks. • Sand and gravel for construction come from sediment. • Sandstone and limestone are used for building stone. • Rock gypsum is used to make plaster. • Limestone is used to make cement. • Salt is used for flavoring. • Phosphate-bearing sedimentary rocks are used for fertilizer. • Quartz sand is used to make glass.

  46. Practice questions on sedimentary rocks

  47. Part 4 Metamorphic Rock

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