Texture The look and feel of an object

Grains Particles of minerals or other rocks. Large grains Small 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 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 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? Crystal shape and size Magnet test- to see if it contains magnetic metals. Acid test to see if the rock includes minerals that contain compounds called carbonates.