Test 2 Chapter 3 Flashcards
Use the rock cycle to explain the statement “One rock is the raw material for another”.
The rock cycle illustrates that any rock type can be transformed into any other rock type. As an
example, igneous rocks may be weathered and compacted into sedimentary rocks. Those
sedimentary rocks may be subjected to heat and pressure to become metamorphic rocks. Depending
on the conditions, rocks can be continually transformed into different types of rock.
What is magma? How does magma differ from lava?
Magma is liquid, molten rock. It is found underground, whereas lava is found extrusively, or outside
Earth’s interior.
In what basic settings do intrusive and extrusive igneous rocks originate?
Intrusive igneous rocks cool below the surface of the Earth. Extrusive igneous rocks cool outside the
Earth’s interior.
How does the rate of cooling influence crystal size? What other factors influence the texture of
igneous rocks?
Faster cooling correlates with smaller crystal size. Other influential factors include the
composition of the magma and the presence of gases, such as in a volcano, which can cause a
vesicular texture.
What does a porphyritic texture indicate about the history of an igneous rock?
A porphyritic texture, where the rock has some large and some small crystals, indicates that the rock
started to cool slowly and then experienced a change of environment or cooling temperature where
the rest of the rock cooled more quickly.
List and distinguish among the four basic compositional groups of igneous rocks
Granitic – felsic or light colored rocks where the dominant minerals are quartz and potassium feldspar.
Andesitic – intermediate rocks where the dominant minerals are amphibole and plagioclase. These are neither light nor dark.
Basaltic – mafic or dark colored rocks with high amounts of magnesium and/or iron. The dominant minerals are pyroxene and plagioclase feldspar.
Ultramafic – these are uncommon rocks with very high amounts of magnesium and/or iron. The dominant minerals are olivine and pyroxene.
How are granite and rhyolite different? In what way are they similar?
Granite has a phaneritic, or coarse-grained texture whereas rhyolite is aphanitic, or fine-grained.
They are compositionally similar, being granitic or felsic rocks. They could be from the same
magma type but the rate of cooling has affected their crystal sizes
What is magmatic differentiation? How might this process lead to the formation of several different
igneous rocks from a single magma?
Magmatic differentiation occurs as magma cools and crystals of minerals with higher melting
temperatures crystallize out of the magma, changing the magmatic composition. By depleting the
magma, or melt, of these minerals, the next rocks to form from the cooling magma will have a
different composition than those that formed at higher temperatures.
Why are sedimentary rocks important?
Sedimentary rocks contain almost all of the fossil record. Sedimentary rocks make up about 75% of
continental rock outcrops and contain clues to the history of the Earth’s surface. They also have
economic importance; for example: limestone used for cement is a sedimentary rock and other
natural resources, including energy resources, are extracted from sedimentary rocks.
What minerals are most abundant in detrital sedimentary rocks? In which rocks do these sediments
predominate?
Quartz and clay minerals, especially from feldspars, are most abundant. These rocks predominate
in conglomerate, breccia, sandstone, arkose, siltstone, and shale.
Distinguish between conglomerate and breccia
Both conglomerate and breccia are made of large-sized sedimentary grains. However,
conglomerate consists of grains that have been rounded before compaction and breccia contains
angular grains of rock and minerals
What are the two groups of chemical sedimentary rocks? Give an example of a rock that belongs to
each group.
The two categories of chemical sedimentary rock are: chemical and biochemical.
A chemical sedimentary rock is travertine limestone. Another is chert. A biochemical rock is
coquina or coal.
How do evaporites form. Give an example.
Evaporites form when minerals are dissolved in solution and the water of that solution evaporates
away. One example is rock salt.
Describe the two processes by which sediments are transformed into sedimentary rocks. Which is
the more effective process in the lithification of sand- and gravel-sized sediments.
The two processes by which sediments are transformed into sedimentary rocks are:
Compaction – where pressure is placed on loosely packed sediment. The volume of the sediment
is reduced and water is squeezed out.
Cementation – when mineral-bearing water circulates among the grains, hardens, and cements
the sediment grains together. This process is most effective for lithifying sand and gravel-sized
sediments.
List three common cements. How might each be identified?
Three common sedimentary cements are:
Calcite – effervesces when a drop of weak HCl is placed on it.
Silica – hardest cement, will scratch glass.
Iron oxide – oxidizes to a rusty red color.
