Properties of Igneous Rocks

Types of Igneous RocksPlutonic / Intrusive: These rocks

formed from magma that crystallized and cooled slowly underground.

These rocks are coarse grained (have visible mineral crystals).

Volcanic – Extrusive RocksExtrusive rocks are formed when

magma or lava cools quickly at or near the surface of the earth.

These rocks have a fine grained or glassy texture. Mineral crystals are either very small or microscopic.

Fine Grained

Glassy Texture

Glassy Texture with many air holes

Coarse grained

Porphyritic Texture

Sometimes magma cools at different depths and temperatures so some mineral crystals are large while others are small.

Magma TypesFelsic magma: Rocks made from this

type of magma tend to be light colored, high in silica and have a large amount of quartz and or feldspar in them.

Mafic magmaThis magma tends to form rocks that

are dark colored, high in ferromagnesian minerals like hornblende, augite, olivine and biotite. (Dark minerals)