GOL 105 Chapter 4 Concept Checks – Flashcards
Unlock all answers in this set
Unlock answersquestion
What is magma? How does magma differ from lava?
answer
Magma is a body of molten rock found at depth, including any dissolved gases and crystals. Lava is magma that reaches the Earth's surface. Magma is intrusive while lava is extrusive.
question
List and describe the three components of magma.
answer
Melt is the liquid portion of magma and has the eight most common elements found in Earth's crust. Solid component is crystals of silicate minerals. Volatiles are the gaseous component of magma that form a gas at surface pressures.
question
Describe the process of crystallization.
answer
The formation and growth of a crystalline solid from a liquid or gas.
question
Compare and contrast extrusive and intrusive igneous rocks.
answer
Extrusive rocks are formed when molten rock solidifies at the surface. Intrusive rocks are formed when molten rock crystallizes at depth.
question
Igneous rocks are composed mainly of which group of minerals?
answer
Silicate Minerals
question
How do light-colored igneous rocks differ in composition from dark-colored igneous rocks?
answer
Light-colored igneous rocks are more granitic (felsic) in composition and contain more feldspar and silica. Dark-colored igneous rocks are more basaltic (mafic) in composition and contain more iron and magnesium.
question
Distinguish among the four basic compositional groups of igneous rocks.
answer
Felsic, Andesitic, Mafic, and Ultramafic composition.
question
How does silica content vary with the abundance of other elements, and how does it affect the behavior of magma?
answer
Rocks with high amounts of silica contain very little iron and magnesium but are rich in sodium and potassium. The more silica in magma, the more viscous the magma is.
question
Define Texture.
answer
Texture is the size, shape, and distribution of the particles that collectively constitute a rock.
question
How does the rate of cooling influence crystal size? What other factors influence the texture of igneous rocks?
answer
Slow cooling promotes the growth of large crystals. Rapid cooling generates small crystals.
question
List this six major igneous rock textures.
answer
Glassy, Aphanitic, Phaneritic, Porphyritic, Vesicular, Pyroclastic.
question
What does a porphyritic texture indicate about the cooling history of an igneous rock?
answer
It indicates that crystals were formed at depth (slow cooling) and then the magma moved to a shallow depth or erupted (fast cooling).
question
The classification of igneous rocks is based largely on two criteria. Name these criteria.
answer
Texture and mineral composition.
question
How are granite and rhyolite different? In what way are they similar?
answer
Rhyolite is the intrusive equivalent of granite. Both are felsic in composition.
question
Classify each of the following as felsic, intermediate, or mafic: gabbro, obsidian, granite, and andesite.
answer
Gabbro is Mafic. Obsidian is Felsic. Granite is Felsic. Andesite is Intermediate.
question
Describe each of the following in terms of composition and texture: Diorite, Rhyolite, and Basalt Porphyry.
answer
Diorite has an Intermediate composition and phaneritic texture. Rhyolite has a Felsic composition and an aphanitic texture. Basalt Porphyry has a Mafic composition and a porphyritic texture.
question
How do tuff and volcanic breccia differ from igneous rocks such as granite and basalt?
answer
Tuff and volcanic breccia are identified with a modifier; for example rhyolite tuff indicates a rock composed of ash-size particles having a felsic composition.
question
What is the geothermal gradient? Describe how the geothermal gradient compares with the melting temperatures of the mantle rock peridotite at various depths.
answer
An increase in temperature with depth. 20-30 degrees Celsius per kilometer. The temperature at which peridotite melts is higher than the geothermal gradient.
question
Explain the process of decompression melting.
answer
It occurs where hot solid mantle rock ascends in zones of convective upwelling, thereby moving into regions of lower pressure.
question
Name two plate tectonic settings in which you would expect magma to be generated.
answer
Divergent Boundary plates and subduction zones.
