ROCKS

ROCKS

1. IGNEOUS ROCKS

   • CLASSIFYING
     • Texture
       • Rough or smooth
       • Size and shape of crystals
       • Air bubbles or any other observable features
     • Colour
       • Dark Coloured (Mafic)
         • Olivine
         • Pyroxene
       • Light coloured (Felsic)
         • Quartz
         • Feldspar
   • HOW ITS FORMED
     • Extrusive Igneous Rock
       • no time for crystals to grow
         • small or no crystals formed
           • Basalt (small visible crystals)
           • Obsidian (No visible crystals)
           • Pumice (Low density, doesn't absorb water)
           • Scoria (Dark, more dense)
     • Intrusive Igneous Rock
       • Time for crystals to grow
         • Big crystals are formed
           • Quartz
           • Feldspar
           • Biotite

2. SEDIMENTARY ROCKS

   • Overlying layers of sediment compact the sediments and force out excess water.
     • Clastic Sedimentary Rock
       • Formed when sediments are laid down by wind, water, ice and gravity
       • Contain broken pieces of other rocks known as clasts
       • Layers are stacked and build up on top of each other as they are deposited
       • Grains don't interlock because they didn't crystallise and grow together in the rock, they are cemented instead.
       • May contain fossils (preserved remains of animals or plants)
       • Classified according to size and nature of rock grains and chemical composition of cement
       • Examples of Clastic Sedimentary Rocks
         • Conglomerate (large rounded rocks cemented between grains that are often microscopic)
         • Breccia (similar to conglomerate but lumps are sharp-edged)
         • Mudstone (particles often microscopic, very soft rock)
         • Sandstone (particles of sand, usually harder than mudstone)
     • Chemical Sedimentary Rock
       • Form when minerals dissolved in groundwater crystallise within the sediments or when water evaporates leaving behind crystals
       • Quite soft, helps distinguish them from harder igneous rocks
       • Examples of Chemical Sedimentary Rock
         • Halite
         • Gypsum
         • Limestone
     • Biogenic Sedimentary Rock
       • Form when dead plant matter or animal remains accumulate and cement together
       • Mostly organisms but contains small amounts of sediments
       • Can be layered and are usually soft
       • Examples of Biogenic Sedimentary Rock
         • Coal
         • Chert
         • Flint

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