The Scheme for Igneous Rock Identification

A Brief Tour

Crystal size Description Grain Size

Igneous rocks have “Intergrown Crystals”

Intergrown

Intergrown

Intergrown

Not Intergrown

Where it was formed Outside the volcano: Extrusive Inside the Earth: Intrusive

Bubbles? Yes= Vesicular

Bubbles? No=Non-vesicular

Color Very Light Light NotVery LightNot Very Dark Dark Very Dark Neither Light nor Dark Lightest Darkest

Density Very Light LightDense Very Dense Medium Density

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

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%

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

Name a coarse-grained, dense rock.

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