Igneous Rocks (1) As you know by now, geologist classify rocks as igneous, sedimentary, or metamorphic. Each rock class implies a process that has led to the formation of the rock and has given the rock observable characteristics. For example, igneous rocks are formed from magma -- molten rock. The effect of crystals growing in a liquid are recognizable in the kinds of minerals found in the rock, the shape of the individual crystals, and the random distribution of the crystals in most igneous rocks. However, although most igneous rocks share important characteristics, they come in a variety of color and textures that imply differences in their chemistry and history.
B. Texture
LIGHT INTERMEDIATE DARK INTRUSIVE
EXTRUSIVE
Coarse Granite and Granodiorite
A. Oceans and Continents B. Intrusive and extrusive
| GRANITIC | ANDESITIC | BASALTIC | |
| TEMPERATURE | |||
| VISCOSITY | |||
| WATER CONTENT |
1. List and describe 3 characteristics that are shared by most igneous rocks and 3 that are likely to vary depending on their chemistry and the environment in which they form.
2. Classify igneous rocks on the basis of texture and color.
3. Explain why intrusive rocks are likely to have larger mineral grains than extrusive rocks.
4. Describe the effect of continental and oceanic crust on the chemistry of igneous rocks.
5. Explain why basalts are much more common than rhyolites.
6. Discuss the importance of temperature and water in the ability of magmas to reach the surface.
7. Explain why andesites might be considered hybrids.