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Rocks

Rocks. Are composed of more than one mineral. Chapter 6 Section 1. Three Major Classes of Rocks. 1. Igneous -formed by cooling and hardening of hot, molten rock (magma) inside Earth.

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Rocks

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  1. Rocks Are composed of more than one mineral Chapter 6 Section 1

  2. Three Major Classes of Rocks 1. Igneous-formed by cooling and hardening of hot, molten rock (magma) inside Earth 2. Sedimentary-formed by the compaction and cementing of layers of sediments (rock fragments, plant and animal remains, minerals that settle out of solution onto lake and ocean bottoms) 3. Metamorphic-formed by the effects of heat and pressure on other rocks BrainPop 3 Types of Rocks

  3. The Rock Cycle • The continuous process that causes rocks to change from one form to another • Caused by interactions between water, air, and land Rock Cycle Movie

  4. ESRT pg. 6

  5. What happens to igneous rocks? 1. Heat and pressure/ “metamorphism” metamorphic rock 2. Melt to form magma which solidifies  igneous rock 3. Weathering and erosion form sediments which are deposited, buried, compacted, and cemented sedimentary rock 3 1 2

  6. What happens to sedimentary rocks? 1. Heat and pressure/ “metamorphism” metamorphic rock 2. Melt to form magma which solidifies  igneous rock 3. Weathering and erosion form sediments which are deposited, buried, compacted, and cemented sedimentary rock 3 2 1

  7. What happens to metamorphic rocks? 1. Heat and pressure/ “metamorphism” metamorphic rock 2. Melt to form magma which solidifies  igneous rock 3. Weathering and erosion form sediments which are deposited, buried, compacted, and cemented sedimentary rock 1 3 2

  8. Igneous Rocks • Form from molten rock or volcanic ash • As magma cools, crystals grow & interlock (rate affects size) Chapter 6 Section 2 Igneous Rock Formation Movie

  9. The Starting Material • Magma may be classified as felsic, mafic, or an intermediate form. • Felsic magma: thick and slow moving; large amounts of silica (SiO2) and small amounts of calcium, iron, and magnesium; typically hardens into rocks containing light-colored silicate minerals (ex. quartz and orthoclase feldspar) • Mafic magma: hotter, thinner, more fluid; large amounts of iron and magnesium and smaller amounts of silica; typically hardens into rocks containing dark-colored silicate minerals (ex. hornblende, augite, biotite)

  10. 2 Groups of Igneous Rocks Intrusive Igneous Rocks • Form from magma which cools slowly deep inside the earth (internal) • Crystals are medium to coarse texture (easily seen) • Form from lava (magma that has exited the crust) that cools quickly (external) • Crystals are very small or not seen at all Extrusive Igneous Rocks

  11. Igneous Rock Descriptions • Igneous Rocks are grouped into families according to mineral composition. • Specific igneous rocks can be recognized by: Color- determined by the mineral composition (makeup) Texture- the size & arrangement of crystals

  12. Granite Family/Felsic Rocks • Form from felsic (silica and aluminum-rich) magmas • Usually coarse-grained because their slow-rising, “sticky” parent magmas tend to cool slowly underground • Typically contain quartz, feldspar, mica, hornblende • Light-colored • Low in density

  13. Granite Family/Felsic Rocks • Granite • one of the coarsest-grained rocks in this family • Intrusive • Often contain large amounts of light-colored feldspar • color of feldspar determines color of the rock • Usually ranges from white or gray to pink • Very common continental rock found in many mountainous areas across the U. S.

  14. Granite Family/Felsic Rocks • Obsidian: • Extrusive • Glassy texture (no crystals) • Chemically similar to granitic rocks even though it is usually dark brown or black • Pumice: • Extrusive • Forms when silica-rich lava hardens as steam & other gases bubble out of it • Vesicular texture • Resembles a sponge because of holes and air pockets • Often able to float on water

  15. Granite Family/Felsic Rocks • Felsite: • General name for any light-colored, fine-grained rock • Rhyolite is a common example • Fine-grained, ranges from light gray to pink

  16. Gabbro Family/Mafic Rocks • Form from mafic (iron and magnesium-rich/silica poor) magmas • Dark in color • High density • Typically contain pyroxene, olivine, plagioclase feldspar (amphibole and biotite mica)

  17. Basalt is igneous rock formed from mafic magma. Gabbro Family/Mafic Rocks • Gabbro: coarse-grained rock. very dark color • Basalt: fine-grained, dark gray or black • Composition similar to gabbro • Most common rock in gabbro family • Makes up the ocean floor • On land, most common rock • formed from lava flows

  18. Gabbro Family/Mafic Rocks • Diabase: texture is finer than gabbro but coarser than basalt • Basalt glass: resembles obsidian but is mafic • Scoria: (like pumice) full of holes, darker and denser than pumice, holes are usually larger, unlikely to float

  19. Diorite Family/Intermediate Rocks • Composition is neither felsic or mafic but has characteristics of both = intermediate • Colors tend to be medium grays and greens (darker than granites and lighter than gabbros)

  20. Diorite Family/Intermediate Rocks • Diorite: coarse-grained, has less quartz than granite and less plagioclase feldspar than gabbro • Andesite: fine-grained

  21. Other Igneous Rocks • Felsic-intermediate: granodiorite • Ultramafic: peridotite, dunite, pyroxenite • Hypothesized to be similar to rocks in Earth’s mantle

  22. Igneous Intrusions • Pluton: any rock mass that forms when magma pushes into fractures (cracks) in the bedrock • Dike: vertical, in between rock layers • Sill: parallel to rock layers it intrudes • Ex. Palisades Sill along the Hudson River (NY/NJ) • Laccolith: domed mass, bulge • Volcanic neck: central plug of hardened magma left after the volcanic material around it has worn away • Batholith: largest of all plutons, cores of many mountains • Stock: a small batholith that is exposed at the surface

  23. Volcanic neck Laccolith Volcano Stock Dike Batholith Sill Igneous Intrusions

  24. Sedimentary Rocks • Made of sediments • Cover most of the crust’s surface • 3 types Chapter 6 Section 3

  25. Clastic Sedimentary Rocks • Formed from fragments of other rock that are moved (usually by running water) • Sediments are deposited layer after layer (as the water slows down) • Sorted by largest sediments first, smallest last • Compacted as layers pile up or cemented together by minerals that are dissolved in the water • Type of cement influences color (silica, calcite, iron oxide, and clay)

  26. Classified by Particle Size Smallest • Silt & Clay particles shale/siltstone • Sand particles sandstone • Mixed particles conglomerate/breccia Largest

  27. Chemical Sedimentary Rocks • Chemical sediments form when minerals precipitate (fall out) of water. • Two ways • Evaporation: Form when a sea or lake dries up leaving behind minerals that were dissolved in water • Chemical action: dissolved ions combine to form new minerals Also referred to as crystalline sedimentary rocks

  28. Chemical Sedimentary Rocks Examples: Rock Salt Rock Gypsum Limestone (travertine)

  29. Organic Sedimentary Rocks • Form from sediments consisting of the remains of plants and animals

  30. Organic Sedimentary Rocks • Shells  Fossil limestone

  31. Organic Sedimentary Rocks • Plant remains  coal peat lignite bituminous anthracite

  32. Features of Sedimentary Rocks • Stratification • arrangement of visible layers • result from changes in sediment type being deposited • Bedding planes (lines between the layers) show where the layers are separated • Usually horizontal, but cross-bedding (angled deposits) can occur • Occur for a number of reasons • New types of rocks picked up (from different locations) • More of different types of rocks carried during flooding • Sediments carried longer or shorter distances

  33. Features of Sedimentary Rocks • Fossils • the remains, impression, or other evidence of a plant or animal preserved in rock • occur when dead organism is buried by sediments and gradually turns to rock • Usually only hard parts are preserved • Impressions occur when shell, skeleton, etc. is pressed into soft sediments

  34. Features of Sedimentary Rocks • Ripple marks = sand patterns formed by the wind, streams, waves, or currents • Mud cracks = develop when wet clay dries and contracts (shrinks) • Cracks fill with different sediments & fossilize

  35. Features of Sedimentary Rocks • Nodules = lumps of fine-grained silica in limestone or chalk • Ex. chert and flint • Concretions = round, solid masses of calcium carbonate • Probably form when minerals in dissolved in water precipitate around shell fragments or other impurities in clay sediments • Ex. oolites • Geodes = spheres of silica rock found in limestone • Inside lined or filled with crystals (quartz or calcite)

  36. Metamorphic Rocks • Formed from “parent rock” • Often resembles “parent rock” • Differences are the result of metamorphic processes that the “parent rock” has undergone

  37. Metamorphic Processes Metamorphism: the process by which a rock’s structure is changed by pressure, heat, and moisture. • Pressure & heat may originate from: • the Earth’s internal heat • the weight of overlying rock • the deformation of rock as mountains build

  38. Metamorphic Processes • A metamorphic rock may have a chemical composition, texture, or internal structure that differs from the parent rock. • Minerals may be enlarged or reformed • New minerals may appear • The rock may be more dense and less porous (less “empty” space)

  39. Metamorphic Processes: Two Basic Types of Metamorphism • Regional • Forms most of the metamorphic rock of Earth's crust • Often occurs over very large areas • Local • Smaller, more distinct areas

  40. Regional Metamorphism • Can occur during mountain building • Large areas of rock metamorphosed • Due to intense heat and pressure • Temperature increases with depth • Pressure increases w/ depth (more overlying rock) • Pressure greater in 1 direction, minerals align in layers • Hot liquids & gases speed up the process • Different amounts of heat & pressure  different amounts of metamorphism. • Can cause folding of rock layers • Higher temperature & pressure  greater metamorphism

  41. quartzite sandstone gneiss schist phyllite shale slate Lime Marble Limestone

  42. Local Metamorphism • Two types • Contact: • Occurs when hot magma moves into rock, heating and changing it. • Causes fewer changes and affects much less rock than regional metamorphism • Deformational: • Occurs at relatively low temperatures and high pressure • Caused by stress and friction (often at faults where rocks move against each other) • Mineral composition usually stays the same, but texture and structure may change

  43. Metamorphic Rock Descriptions • Description and identification usually based on parent rock, mineral content, and texture • 2 types • Foliated • Non-foliated

  44. Metamorphic Rock Descriptions • Foliated Metamorphic Rocks • Minerals flattened by pressure producing mineral alignment or (different colored) bands • May look scaly • Often split along parallel layers

  45. Foliated Metamorphic Rocks: Examples Granite  gneiss Shale  Slate  Phyllite  Schist (Extreme Metamorphism)

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