ROCKS

ROCKS

IGNEOUS ROCKS
1. CLASSIFYING
  1. Texture
    1. Rough or smooth
    2. Size and shape of crystals
    3. Air bubbles or any other observable features
  2. Colour
    1. Dark Coloured (Mafic)
      1. Olivine
      2. Pyroxene
    2. Light coloured (Felsic)
      1. Quartz
      2. Feldspar
2. HOW ITS FORMED
  1. Extrusive Igneous Rock
    1. no time for crystals to grow
      1. small or no crystals formed
        Basalt (small visible crystals)
        Obsidian (No visible crystals)
        Pumice (Low density, doesn't absorb water)
        Scoria (Dark, more dense)
  2. Intrusive Igneous Rock
    1. Time for crystals to grow
      1. Big crystals are formed
        Quartz
        Feldspar
        Biotite
SEDIMENTARY ROCKS
1. Overlying layers of sediment compact the sediments and force out excess water.
  1. Clastic Sedimentary Rock
    1. Formed when sediments are laid down by wind, water, ice and gravity
    2. Contain broken pieces of other rocks known as clasts
    3. Layers are stacked and build up on top of each other as they are deposited
    4. Grains don't interlock because they didn't crystallise and grow together in the rock, they are cemented instead.
    5. May contain fossils (preserved remains of animals or plants)
    6. Classified according to size and nature of rock grains and chemical composition of cement
    7. Examples of Clastic Sedimentary Rocks
      1. Conglomerate (large rounded rocks cemented between grains that are often microscopic)
      2. Breccia (similar to conglomerate but lumps are sharp-edged)
      3. Mudstone (particles often microscopic, very soft rock)
      4. Sandstone (particles of sand, usually harder than mudstone)
  2. Chemical Sedimentary Rock
    1. Form when minerals dissolved in groundwater crystallise within the sediments or when water evaporates leaving behind crystals
    2. Quite soft, helps distinguish them from harder igneous rocks
    3. Examples of Chemical Sedimentary Rock
      1. Halite
      2. Gypsum
      3. Limestone
  3. Biogenic Sedimentary Rock
    1. Form when dead plant matter or animal remains accumulate and cement together
    2. Mostly organisms but contains small amounts of sediments
    3. Can be layered and are usually soft
    4. Examples of Biogenic Sedimentary Rock
      1. Coal
      2. Chert
      3. Flint

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	Created by Hamideh Mirzad about 7 years ago