Ch. 6.2. Igneous Rocks

1. Intrusive igneous rock: formed from the cooling and solidification of magma beneath Earth’s surface 2. Extrusive igneous rock: formed from the cooling and solidification of lava at Earth’s surface

The Formation of Magma 3 factors influence rock melting: - temperature - pressure - presence of fluids in the rock (such as water)

Partial Melting Minerals with lower melting points are the first minerals to melt. As the temperature increases and as other minerals melt, the magma’s composition changes.

Chapter 6 The Formation of Magma

Fractional Crystallization Minerals that have the highest freezing points crystallize first. When magma cools, the cooling process is the reverse of the process of partial melting.

Chapter 6 The Formation of rocks

A. Intrusive Igneous Rock Structures Batholiths: intrusive formations that spread over a large area Stocks: similar to batholiths but smaller Sills: layers of rock parallel to the layers of rock that surround it. Dykes: new layers cutting across existing layers.

B. Extrusive Igneous Rock Structures Volcano: a vent through which magma, gases, or volcanic ash is expelled. Lava flows, lava plateaus, and tuff layers

Igneous Rock Magma Melting Solidifying Texture Fractional Crystallization Intrusive Extrusive Partial Melting

Textures of Igneous Rocks: Coarse-Grained Rocks cooled slowly, have large mineral crystals b. Fine-Grained rocks cooled fast, have small grains.

c. porphyritic texture: magma cooled slowly at first, but then cools more rapidly as the magma nears or reaches Earth’s surface large crystals together with smaller crystals.

d. vesicular texture Contains bubbles of gases

e. glassy texture: highly viscous magma cooled very rapidly No large crystals

Composition of Igneous Rock Felsic Rock: - rich in feldspars and silica - light in color. Ex: granite, rhyolite, obsidian, and pumice.

2. Mafic Rock - rich in magnesium and iron, dark in color. Example: basalt and gabbro.

3. Intermediate Rocks: proportions of silica between felsic and mafic. Examples: diorite and andesite.

Intrusive vs. extrusive igneous rock