Chapter 4-2 Igneous Rocks

They cool and crystallize from molten rock - Two kinds:

Intrusive- form from magma

cooling inside Earth

Extrusive- form from

cooled lava outside Earth

 
Intrusive (within crust)

Extrusive (above ground)
Composition:
Quartz (SiO2) & Feldspar
Ca, Fe, Mg
Color:
generally light

generally dark

Texture:
coarse (slow cooling)
medium, or fine (fast cooling)
Movement:
usually slow and thick
usually fast and thin

 

Felsic and Mafic Rocks
Felsic- light-colored, high silica, intrusive rocks. example: Granite

Mafic- dark-colored, low silica, extrusive rocks. The molten rock (lava) is hotter, thinner, and more fluid than the molten rock (magma) that forms the felsic rocks. examples: Basalt, Diorite

 
Families of Igneous Rocks

1.) Granites- high silica and feldspar

2.) Gabbros- low silica, olivine, hornblende, biotite
3.) Diorites- intermediate in composition
Porphyritic- fine and coarse-grained due to 2 stages of cooling.

 

Small grains = fast cooling

Large grains = slow cooling