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

2. 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

3. 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

4. Mafic
Felsic
Andesditic
Ultramafic
Igneous compositions

5. Pg. 99 Essentials of Geology textbook Figure 4.5
IgneousCompositionClassification.html

6. 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

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

8. Types of textures Aphanitic (fine-grained) Phaneritic (coarse-grained)
Porphyritic
Vesicular
Glassy
Pyroclastic
_geo/smartfigure/sf-IgneousTextures.html