The Scheme for Igneous Rock Identification

A Brief Tour

Crystal sizeDescription

Grain Size

Intergrown Crystals

Intergrown

Intergrown

Not Intergrown

Where it was formedOutside the volcano: Extrusive

Bubbles? Yes= Vesicular

Bubbles? No=Non-vesicular

ColorVery Light

LightNotVery LightNot Very Dark

DarkVery Dark

Neither Light nor Dark

Lightest

Darkest

DensityVery LightLight DenseVery Dense

Medium Density

Finding The MineralsIdentify 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-grainedrock with no bubbles.

Name a coarse-grained, dense rock.

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