Texture The look and feel of an object

Texture • The look and feel of an object

Grains • Particles of minerals or other rocks. • Large grains – Coarse feeling • Small grains – Fine feeling

What is an Igneous Rock? • Forms from the cooling of magma or lava.

Classifying Igneous Rocks • Origin • Texture • Mineral Composition

Origin: Intrusive vs. Extrusive • Intrusive – Igneous rock that formed when magma hardened beneath Earth’s surface. • Extrusive – Igneous rock that formed from lava that erupted onto Earth’s surface.

Texture of Igneous Rocks • Depends on… – Size and shape of mineral crystals. • Large grains – Coarse feeling • Small grains – Fine feeling

Texture of Igneous Rocks • Texture: – Rapidly Cooling = Extrusive • Forms fine-grained igneous rocks with small crystals – Slowly Cooling= Intrusive • Forms coarse-grained igneous rocks with varied sizes of crystals.

Extrusive • Rapidly cooling lava that erupted onto Earth’s surface. • Rapidly cooling = fine-grained crystals. Obsidian

Intrusive • Slow cooling magma that hardens beneath Earth’s surface. • Slow cooling = large, coarse-grained crystals that vary in size and shape. Porphyry

How Do Geologists Determine Mineral Composition? 1. Crystal shape and size 2. Magnet test- to see if it contains magnetic metals. 3. Acid test to see if the rock includes minerals that contain compounds called carbonates.