Classroom of Money and Wisdom for Earth Science

Lecture 1 The Rock

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Lecture 1 The Rock

What is Rocks?

A rock is a naturally occurring solid mixture of one or more minerals or organic matter

Rocks are classified by how they are formed, their composition, and their texture

Rocks change over time through the rock cycle

Igneous rock begins as magma.

Lecture 1 The Rock

Lecture 1 The Rock

Magma can form:

  • When the rocks are heated
  • When pressure is released
  • When rocks change their composition
  • Magma freezes between 700 °C and 1,250 °C
  • Magma is a mixture of many minerals

Types of Igneous Rocks

  • Felsic: light-colored rocks that are rich in elements such as aluminum, potassium, silicon, and sodium
  • Mafic: dark-colored rocks that are rich in calcium, iron, and magnesium, poor in silicon
  • Coarse-grained:  takes longer to cool, giving mineral crystals more time to grow
  • Fine-grained: cools quickly with little to no crystals 

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