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Rocks

Rocks . Ch-6. Law of Uniformitarianism. The processes that have occurred in the past are the same ones as are happening today Ex) the erosion rate that you see today is probably the same as what it was like in the past Landforms form most of the time over long periods of time

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Rocks

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  1. Rocks Ch-6

  2. Law of Uniformitarianism • The processes that have occurred in the past are the same ones as are happening today • Ex) the erosion rate that you see today is probably the same as what it was like in the past • Landforms form most of the time over long periods of time • It was thought that landforms were caused by catastrophic events • Ex) a large canyon would be formed over a short time by a large flood

  3. Types of Rocks • Igneous • formed when molten material (magma) cools and forms a rock • Sedimentary • When pieces of rock are put together and form one rock • Metamorphic • when a rock that already exists gets changed into another type by heat and/or pressure

  4. Rock cycle

  5. Formed by the cooling of molten rock Molten rock can be Lava molten rock found at the surface Magma molten rock found anywhere Igneous Rocks

  6. Felsic magma Thick and slow moving Contains large amount of silica Usually hardens into light colored rocks Explosive eruptions Mafic magma Hotter and thinner Contains low amount of silica Usually hardens into dark colored rocks Gentle eruptions Types of Molten material

  7. coarse grained Also called intrusive or Plutonic large crystals from forming deep in the earth and cooling slow enough for the crystals to grow large. Fine grained Also called extrusive or volcanic small crystals from forming at the earths surface and cooling to quickly for crystals to grow. Porphyry has both small and large crystals because it started to cool inside the earth then was sent out and cool at a different rate. Three grain textures

  8. Granite family Formed from felsic magmas Light colored Can have any grain Appears at surface only after uplifting or erosion Examples – granite, obsidian, pumice and rhyolite Gabbro family Formed from mafic magmas Dark colored High density Examples – gabbro, basalt (ocean floor)and scoria Diorite family Has properties of both previous groups so deserves its own group Families of igneous rocks

  9. Dike A vertical or steep angled sheet of magma that cuts across the existing rock layers as it cools into a rock Sill A horizontal sheet of magma that runs parallel to the existing rock layers as it cools into a rock Lacolith when the magma is too thick too flow out so it builds up into a bulge -causes the layers above it to bulge as well Volcanic neck the remains, after erosion, of the central plug of hardened magma from a volcano Types of Plutons (rock masses that cooled underground)

  10. Batholith • largest of all plutons • form core of many mt ranges • usually made of granite

  11. Sedimentary rocks • Formed by sediments being buried and compressed. • Form in layers (Law of Superposition) • oldest layers on the bottom, newest on top • If no overturning has Occurred • Sediments get sorted so most are formed by material of the same size.

  12. Clastic Formed from fragments of other rocks Cementation occurs Sediments are usually sorted by water Gravels form conglomerates Sands form sandstones Silts form clays Chemical Form when mineral grains fall out of solution or evaporate Example - rock salt (halite) Organic Form from the remains of plants and animals Ex) – coal (plants) some limestones (shell fragments) Three Types of Sed. Rocks

  13. Fossils Types of Fossils #1 Original remains When the organism is preserved in something like ice or sap (examples insects in sap or woolly mammoths in ice) #2 Replaced remains The soft parts decay and are filled back in by minerals (example – petrified wood) #3 Mold and cast The soft parts buried and an impression is made in the material. The soft parts then waste away and you are left with an empty cavity that looks like the organism. #4 Trace fossils Impressions left behind that form in rock such as footprints burrows etc. Special Structures

  14. Special Effect cont. • ripple marks • water ripples left in mud then dry • mud cracks • mud dries and cracks the forms into a rock

  15. Metamorphic Rocks • When a rock gets heat and or pressure added to it and turns into a new type of rock. • Doesn’t completely melt but comes close • Minerals line up and get into layers

  16. Types of Metamorphism • #1 Dynamic metamorphism (regional metamorphism) • When Earth’s large plates move the friction or collisions build up enormous heat and pressure and change the rock • Most metamorphic rocks are formed this way • #2 Thermal metamorphism (contact metamorphism) • When magma gets into rock layers it changes the rocks it comes in contact with.

  17. Examples of metamorphism • granite (Igneous) becomes gniess • shale (Sed) becomes slate • limestone (Sed) becomes marble

  18. Rock cycle • Shows how the same material can go through several changes and become all three types of rocks over and over again.

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