Igneous Rocks

What is a Rock? Rocks are known as an aggregate of minerals. In other words, they are made from minerals and most rocks contain several different minerals.

Rocks that form above the surface are called… Lava Volcanic Rocks Basalt Pumice Obsidian Rhyolite Rocks that form below the surface are called… Plutonic Rocks Granite Gabbro Magma

Volcanic Rocks Plutonic Rocks They are intrusive They are extrusive. They have large crystals. They cool slowly They are extrusive. They have small crystals. They cool quickly.

Igneous rocks have intergrown crystals that fit together like a jigsaw puzzle. Granite

NOT the same as cemented together sediments. NOT IGNEOUS Breccia

You’re looking mighty fine baby! Texture: Defines the appearance of an igneous rock. You’re looking mighty fine baby! Rocks can be coarse grained, fine grained or glassy.

Slow cooling results in large crystals that are visible to the eye. Coarse Granite Diorite Gabbro

Faster cooling results in smaller crystals that are only visible under a microscope. Fine Grained Basalt Rhyolite Andesite t

Very rapid cooling causes rocks to have a glassy texture. Obsidian

Let us take a look at page 6 of your ESRT’s and find all the properties of Granite

Texture

Density

Color

Compostion

Intrusive or Extrusive

Plutonic or Volcanic

Minerals

Grain Size

Bubbles? Yes= Vesicular

The Scheme for Igneous Rock Identification

Finding The Minerals Unless you have other information, work in the middle of the rock’s box. Identify the rock.

This is the amount of Potassium Feldspar in the rock.

This is the amount of Quartz in the rock.

This is the amount of Plagioclase Feldspar in the rock.

Use tick marks on a scrap paper to measure the percentage. Potassium Feldspar 25% Quartz 40%

Name a light-colored, fine-grained rock with no bubbles. Practice

Name a coarse-grained, dense rock.

Name a very light-colored, glassy, extrusive rock with bubbles.

Important Concept for Plate Tectonics: Granite (less dense igneous rock) makes up continental crust! Basalt (more dense igneous rock) makes up oceanic crust. SO oceanic crust is more dense than continental crust!