I. Igneous Rock – formed from molten Earth materials

A. Magma is found at the mantle boundary

B. There are typically 4 types of magma related Igneous Rocks

1. Intrusive Igneous Rock – formed from magma that is trapped beneath the surface; the slow cooling allows for crystal growth which give it a coarse grained appearance

2. Extrusive Igneous Rock – when the magma is released, now called Lava, cools quickly to form a fine grain

3. Granititc Magma – thick and stiff due to it’s high silica content

4. Basaltic Magma – very dark magma and is high in Iron

C. Grain size is also useful in classification

1. Porphyry is when a rock has 2 or more grain sizes