Ch 4- Essentials of Geology Igneous rocks Ch 4- Essentials of Geology

Igneous processes Extrusive rocks Intrusive rocks VOLCANIC magma solidifies at the surface Fine-grained Ex: basalt, pumice Oceanic islands: Hawaiian chain and Aleutian Islands Intrusive rocks PLUTONIC magma crystallizes at depth Coarse-grained Ex: granite, diorite

Igneous compositions Igneous rocks are composed mainly of silicate minerals 98% of most magmas Al, Ca, K, Mg, Fe Ferromagnesian-(dark silicates)- rich in iron and/or magnesium, comparatively low in silica Nonferromagnesian-(light silicates)- contain greater amounts of potassium, sodium, and calcium rather than iron and magnesium

Mafic Felsic Andesditic Ultramafic Igneous compositions

Pg. 99 Essentials of Geology textbook Figure 4.5 http://media.pearsoncmg.com/bc/bc_0media_geo/smartfigure/sf- IgneousCompositionClassification.html

Granitic (felsic) vs. Basaltic (mafic) Granitic compositions- Dominant minerals  quartz and potassium feldspar Felsic feldspar and silica (quartz) Basaltic compositions- 45% dark silicate minerals Calcium rich plagioclase (no quartz) mafic magnesium and ferrum

Other compositional groups Andesitic Composition Intermediate Composition Andesite 25% dark silicates mineral Ultramafic Composition composed almost entirely of ferromagnesian minerals Upper mantle

Types of textures Aphanitic (fine-grained) Phaneritic (coarse-grained) Porphyritic Vesicular Glassy Pyroclastic http://media.pearsoncmg.com/bc/bc_0media _geo/smartfigure/sf-IgneousTextures.html