Chapter 3 – 2 Igneous Rocks!

Chapter 3 – 2 Igneous Rocks!

What makes a rock IGNEOUS?

Origin, texture and mineral composition.

ORIGIN: Where the rock is formed.

Extrusive Rock is igneous rock formed from lava that erupted onto Earth’s surface.

Basalt is the most common extrusive igneous rock. Forms much of Earth’s land

and ocean floor.

Intrusive Rock is igneous rock that formed when magma hardened beneath the Earth’s surface.

Granite is the most common form of intrusive igneous rock. Granite forms the

core of many mountain ranges.

Texture of Igneous Rock – Depends upon the size and shape of its mineral crystals.

Rapid cooling forms fine grained, small crystal igneous rock.

Slow cooling magma forms coarse grained rock with large crystals.

Intrusive have larger crystals than extrusive.

Small crystal rocks that appear to have rocks of larger crystals inside them are said

to be PORPHYRITIC.

A change in the rate of cooling creates Porphyritic Rock.

Mineral Composition of Igneous Rocks. Most of Earth’s minerals contain silica (sand). Rocks containing silica are usually light colored.

Dark colored rocks, like basalt contain a mineral called feldspar and usually have

very little silica.

Uses of igneous Rock

• Obsidian – Cutting tools• Granite – Building materials• Basalt – Crushed for construction gravel• Pumice – Abrasives for cleaning and polishes• Perlite – (heated obsidian) Soil additives