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Rocks. Chapter 4. Classifying Rocks. Mineral Composition - Look with a magnifying glass to determine the mineral that makes up the rock Color - Light or dark color, glassy? Texture – look and feel of the rocks surface Grain size – Fine, coarse or no visible grain

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Chapter 4

classifying rocks
Classifying Rocks
  • Mineral Composition - Look with a magnifying glass to determine the mineral that makes up the rock
  • Color - Light or dark color, glassy?
  • Texture – look and feel of the rocks surface
    • Grain size – Fine, coarse or no visible grain
    • Grain Shape – Rounded or jagged
    • Grain Pattern – non-banded, banded
  • What is a rock?
  • mixture of minerals, mineraloids, glass or organic matter
  • 3 Types of Rocks:
  • 1. Igneus Rock – molten material inside earth or from a volcano cools slowly due to the insulation of rock allowing the atoms to arrange themselves into large crystals called mineral grains
Remember: magma forms from great temperatures (1400oC) and pressure in the earth this melts the minerals and forms magma
  • When magma flows to the surface it is called lava
intrusive rocks
Intrusive Rocks

Intrusive Rocks– formed when magma insulated and trapped below the earth surface, holds heat and cools slowly – large mineral grains

  • Granitic – light colored rocks, lower density contains a lot of silicon and oxygen, mountains
extrusive rocks
Extrusive Rocks
  • Extrusive Rocks – Formed when magma cools on the earths surface and cools rapidly – fine grained texture Basaltic – dense, heavy, dark colored (magma) examples iron, magnesium, covers ocean floorCombination:Andresitic – in between basaltic and granitic in mineral composition
igneous rocks texture
Igneous Rocks - Texture
  • Intrusive—Large crystals
  • Extrusive—Small Crystals (maybe not visible: obsidian & Pumice)
  • Mafic—Dark
  • Felsic—Light
sedimentary rock
Sedimentary Rock
  • Sedimentary rock -comprises 75 % rocks on earth -formed when sediments pressed or cemented together – may form layers
    • Sediments – loose materials such as rock fragments, grains and bits of plant and animals
    • Compactation – pressure causes sediments to form rock
    • Cementation – water dissolves minerals (quartz, calcite, hematite, limonite) natural cements
Classification of sedimentary rock:
    • Clastic – broken, named for size & shape of sediments example – conglomerate, breccia, sandstone, shale
    • Chemical – minerals precipitated from a solution or evaporates example – limestone, rock salt
    • Organic – from once living things examples – coal, chalk
sedimentary rocks
Sedimentary Rocks
  • Compacted or Cemented (layering is key)
    • Sandstone
    • Shale
    • Coal (rock or not? Some debate)
  • Clastic
    • Breccia—sharp angles
    • Conglomerate—rounded edges (concrete)
    • Coquina—Shells
coral reefs
Coral Reefs
  • Formed from skeletons of tiny coral animals that grow together to form the coral reef structure
  • Almost all coral reef growth occurs within the top 40 meters of the surface where sunlight penetrates
  • Coral organisms need warm water, found only in tropical oceans
  • Limestone deposits formed from coral reefs
metamorphic rock
Metamorphic Rock
  • Metamorphic rock – rocks changed due to temperature and pressure increases or change in composition
  • Classification of Metamorphic Rock
    • Foliated – mineral grains flatten and line up in parallel bands Example slate and gneiss
    • Slate forms from shale which is arranged in layers when exposed to heat and pressure
    • Nonfoliated – no banding occurs, the mineral grains change, grow and rearrange but no bands Example is marble which forms from sedimentary rock calcite – shiny. Hornblende and serpentine – green. Hermatite - red
metamorphic rocks
Metamorphic Rocks
  • Gneiss—Zebra strips
  • Schist—Metallic shine
  • Marble—Contains Calcite (bubbles w/HCl)
  • Or Morphed sedimentary rock
    • Slate (shale that has hardened)