IGNEOUS ROCKS

TABLE 1. CLASSIFICATION OF COMMON IGENOUS ROCKS

Environment Rock Name

Extrusive(Volcanic)

fine-grained

Instrusive(Plutonic)

coarse-grained

FELSIC MAFIC ULTRAMAFIC

Granite Granodiorite Diorite Gabbro PeridotiteDunite

Pegmatite(VERY coarse

grained)

Rhyolite

COMPOSITION:

Dacite Andesite Basalt

Pumice(vesicular texture)

Scoria(vesicular texture)

Obsidian(glassy texture)

Basaltic Glass(glassy texture)

TABLE 2. MINERAL COMPOSITION FOR IGNEOUS ROCKS

Mineral FELSIC MAFIC ULTRAMAFICQuartz

K-FeldsparPlagioclase

Muscovite

AmphibolePyroxene

Olivine

BiotiteCa-richNa-rich

The classification and identification of igenous rocks is tied in part to the minerals that make up igenous rocks, along with the grain (or crystal) size. The charts below list 15 igenous rocks and 8 common igenous minerals. Your goal for this station is to identify the unkown igneous rocks in front of you. There should be hand lenses available to help see the minerals.

It will make most sense to learn the 8 minerals below at the mineral station prior to working towards identifying your unknown rock samples.

If you are able to identify and understand the mineral composition of these 15 igenous rocks you will know about as much about igenous rocks as anyone who has ever taken an introductory level geo course - or maybe even more!