Igneous Rock . . .

Two types of molten rock:

Igneous Rocks

Felsic

Mafic

High in silicates

Low in silicates

slow flowing

light color

fast flowing

dark color

Molten Rock:Rocks made:

Igneous RocksFelsic Mafic

Granite

Hornblende

• Above the surface− Extrusive or volcanic.− Cools and solidifies

quickly.− Crystals with small grain

size or no crystals at all (glass).

− Can also show air gaps from bubbles. Relatively light.

Igneous RocksForm in 2 places:

Igneous Rocks• Below the surface

− Called intrusive or plutonic.

− Cools and solidifies slowly.− Shows crystals with large

grain size.

Volcanic Rock

Plutonic Rock

Igneous RocksDescriptive Terminology of Rock

Texture•Texture: the size, shape, and arrangement of the mineral crystals in the rock.

•Porphyry: Large crystals are surrounded by a fine-grained mass of rock. It can also have bubbles.

•Frothy: Rocks with no crystals/minerals visible. Has many air gaps (bubbles) and has a foamy appearance.

Igneous RocksDescriptive Terminology of Rock

Texture•Fine Grain: Small, barely visible crystals. Seen with the aid of a magnifying glass.

•Coarse Grain: Large crystals, visible with the un-aided eye, of various minerals in the rock together.

•Glassy: Rocks with no crystals and a clear or translucent appearance.

Frothy Porphyry

Coarse Grain Fine Grain

Obsidian (Black Volcanic Glass)Pumice (Frothy and porous)

Scoria (Frothy and porous)