Introduction to different rock types

Introduction to different rock types

Igneous Rocks

  • Igneous rocks are formed when molten rock cools and hardens.
  • Igneous rocks have crystals. The large crystals are formend in rocks that cooled slowly (deep in the crust). The small crystals are found in rocks that have cooled quickly on the surface.
  • Plutonic igneous rocks are formed when magma cools within the earth’s crust. eg. granite.
  • Volcanic igneous rocks are formed when molten rock cools and hardens on the surface. eg. basalt.

Formation of Granite – Plutonic Rock

  • Formed from magma deep within fold mountains(destructive boundaries).
  • Maga raises to the buckled and folded rock to form batholiths.
  • This maga cools very slowly to create crystals of mica, feldspar and quartz (these three materials form granite).

Formation of Basalt – Volcanic Rock

  • Basalt is formed when magma is cooled quickly on or near the surface.
  • Basalt is a dark heavy rock and may have rusty spots because of its high iron content.

 

Sedimentary Rocks

  • Sedimentary rocks form from sediments of other rocks which have been weathered and eroded.
  • These sediments are compressed and compacted in layers.
  • Examples of organic sedimentary rocks: Coal and limestone.
  • Examples of non-organic sedimentary rocks: Sandstone and shale.

 

Metamorphic rocks

  • Metamorphic rocks are rocks that have been changed from igneous and sedimentary rocks due to heat and/or pressure. This process is called metamorphism.
  • These rocks are formed where plates collide.
  • Compression and collision of the plates creates heat and pressure.

Examples

  • Limestone is changed to marble.
  • Sandstone changed to quartzite.
  • Shale changed to slate or schist.

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