Chapter 3 Homework Questions
1. What is magma? How does magma differ from lava?
Magma is molten rock found beneath the surface of the Earth. Lava is magma that has reached the surface of the Earth. It’s usually hotter and less viscous than magma.
2. List and describe the three components of magma. Silicate, Crystals, Gases
3. How do light-colored igneous rocks differ in composition from dark-colored igneous rocks?
Light-colored igneous rocks are composed of minerals with high silica content, such as quartz and feldspar. Dark-colored igneous rocks are composed of minerals with low silica content, such as olivine and pyroxene.
4. Define texture.
Texture is the size, shape, and arrangement of the mineral grains in a rock.
5. List six major igneous rock textures.
Aphanitic, Phaneritic, Porphyritic, Vesicular, Spheroidal, Columnar
6. The classification of igneous rocks is based largely on two criteria. Name these criteria.
Composition and Texture
7. What is the geothermal gradient?
The geothermal gradient is the rate at which temperature increases with depth in the Earth's crust.
8. Explain the process of decompression melting.
Decompression melting occurs when rock is subjected to a decrease in pressure. This can happen when rock is uplifted to the surface of the Earth, or when it is squeezed into a smaller volume. 9. Define Bowen’s Reaction Series.
Bowen's Reaction Series is a model that describes the sequence in which minerals crystallize from magma as it cools. The series is divided into three zones:
The olivine-pyroxene zone The amphibole-plagioclase zone The biotite-muscovite zone
10. Describe dike and sill, using the appropriate terms from the following list: massive, discordant, tabular, and concordant.
A dike is a tabular igneous intrusion that cuts across the surrounding rock. A sill is a tabular igneous intrusion that is concordant with the surrounding rock.
