Types of Metamorphic Rock

How metamophism effects different different types of rock

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  • Types of Metamorphic Rock
    • Metamorphism of Sandstones
      • Sandstones  vary in type but always have a high proportion of quartz
        • Under the effects of heat and pressure grains tend to interlock and recrystallize to form metaquartzite.
      • The colour of metaquartzite may may indicate how the original       sandstone was cemented.
        • Example: A reddish metaq. is likely to have come from a sandstone which has been cemented with iron minerals
    • Metamorphism of Limestones
      • Limestone's form in a variety of ways but always contain calcite as their main mineral
        • Both Regional and Thermal metamorphism can cause this calcite to recrystallise and form marble
        • Pure Limestones form bright white marble with a sugary texture of interlocking calcite crystals.
        • Muddier types of limestone tend to produce marbles with patches or streaks of coloured minerals from the recrystallisation of their clay minerals
    • Metamorphism of Mudstones and Shales
      • Mustones and shales are fine-grianed sediments composed of complex clay minerals. Different conditions can  change these rocks in different ways.
      • During Thermal Met. rocks close to the intrusion have complete recrystallisation so the resulting rock has an interlocking texture creating hornfels.
        • Further away  less change occurs and spotted rocks are formed. the "spots" are new minerals which have been able to form.

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