Download Geology Winter 09 Study Guide – Igneous Rocks • Lava flows are

Geology Winter 09
Study Guide – Igneous Rocks
• Lava flows are typically finer grained than intrusive igneous rocks. Why?
• What type of magma is most likely to quench (congeal) to a natural glass? What are the characteristics.
• Sizes, shapes, and arrangements of mineral grains and other rock-forming constituents comprise what
basic aspect of igneous rocks?
• What texture describes how magma cools and consolidates without growth of mineral grains
• What texture describes how mineral grains are of roughly equal size and coarse enough to be seen
without a microscope or magnifying glass
• What texture describes how rock has two or more, distinctly different-sized populations of mineral
grains
• What texture describes how a magnifying glass or microscope is needed to see individual mineral grains
• What is an open cavity in a volcanic rock that was filled by a gas bubble when the lava was still mainly
liquid called?
• Consider Bowen's reaction series. Which mineral would you expect to see as a phenocryst in a
porphyritic basalt?
• What is the equivalent aphanitic or phanertitic rock to granite?
• What is the equivalent aphanitic or phanertitic rock basalt?
• What is the equivalent aphanitic or phanertitic rock diorite?
• What igneous rocks exhibit aphanitic texture?
• In a porphyritic volcanic rock, which mineral grains are the last to crystallize?
• Visible quartz and potassium feldspar grains are the main constituents in which igneous rock?
• What igneous rocks have a pyroclastic texture?
• Which rocks have an extremely vesicular, volcanic glass?
• Which igneous rocks are composed mainly of ferromagnesian minerals?
• Which minerals crystallize early in Bowen's reaction series?
• What is the dominant feldspar in basalt?
• Diamonds occur mainly in which of the following geologic settings?
• What do geologists look at under a microscope?
• Which igneous rocks are characterized by very coarse mineral grains?
• What are vesicles?
• What texture shows a single, long period of cooling and crystallization?
• What has the same mineral composition as andesite?
• What do pumice and obsidian have in common?
• Describe an aphanitic texture?
• Which igneous rocks exhibit phaneritic texture?
• Which texture would be most unlikely to occur in an extrusive igneous rock?
• Which igneous texture indicates two, distinctly different sizes of mineral grains?
• Which phaneritic, igneous rock is comprised mainly of olivine, pyroxene, and calcium plagioclase?
• What igneous rock is named for a prominent, volcanic mountain range in western South America?
• What is the dominant lava type erupted from volcanoes in Hawaii and Iceland?
• Which igneous rock or magma has the lowest silica (SiO2) content?
• Which of the following igneous rocks is thought to be common in the Earth's mantle but rare in the
crust?
• What small, intrusive igneous rock bodies often contain gem-quality crystals of minerals such as beryl
and tourmaline and high concentrations of relatively rare elements such as lithium, boron, and
beryllium?
• What weight percentage of silica (SiO2) typifies granites and rhyolites?
• What term denotes the larger mineral grains in a porphyritic igneous rock?
• What general term denotes molten rock below the Earth's surface?
• What type of magma, commonly erupted along oceanic ridge systems, originates by partial melting of
mantle peridotite?
• Pegmatites consist of what size mineral grains?
• What igneous texture refers to rocks composed mainly of mineral and volcanic fragments?
• An important reaction series showing the expected order in which minerals crystallize from magma was
named for its originator. Who was he?
Ig_Rk_SG
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Name two igneous rocks with glassy textures.
What type of igneous rock is both glassy and highly vesicular?
Which process describes how the removal and isolation of early-formed mineral grains can cause the
composition of the remaining magma to change?
Igneous rocks are classified on the basis of what two main characteristics?
What igneous rock comprises the active volcanoes of Hawaii and Iceland?
What are the igneous textures?
What are the igneous compositions?
How does temperature changes affect mineral crystallization?
What is the most abundant type of magma erupted at oceanic spreading centers?
"Ignis" in Latin means _________.
____________ rocks cool and crystallize directly from molten rock.
More than _______ percent of the Earth's outer 30 miles consists of igneous rock.
True or False? Most igneous rock solidifies when it reaches the surface of the Earth, as it is exposed to
water or air.
_________ is molten rock that flows within the Earth.
True or False? To be called magma, the rock materials must all be in a liquid state.
_________ is molten rock that flows above ground.
Crystals grow until they touch the edges of adjacent ______________.
The slower a magma or lava cools, the (circle one: larger smaller) the crystals it contains.
With phaneritic texture crystals may be seen with a(n):
1. unaided eye
2. magnifying glass
3. light microscope
4. electron microscope
Magmas that enter preexisting rocks form _____________ rocks which, if found deep below the surface
are also known as plutonic rocks.
Igneous rock that has exceptionally large crystals (sometimes several meters long) is most likely:
1. aphanitic
2. obsidian
3. pegmatic
4. phaneritic
Igneous rocks like basalt have _____________ textures because their crystals cannot be seen with the
unaided eye.
Igneous rocks with ______________ texture have large, often perfect crystals surrounded by regions
with much smaller or even invisible grains.
The texture of an igneous rock may be phaneritic, pegmatic, aphanitic, porphyritic, or _________ (such
as obsidian and pumice).
____________, a light-colored volcanic glass, forms when bubbling, highly gaseous, silica-rich magma
cools instantaneously. It is sometimes light enough to float on water.
____________, a dark volcanic glass, forms when silica-rich magma cools instantaneously. It breaks by
fracture rather than cleavage and was used by prehistoric humans to fashion cutting tools.
True or False? Felsic minerals melt at a lower temperature than mafic minerals.
True or False? Felsic rock can be produced from mafic magma.
The most important factors controlling the creation of magma are:
1. pressure, heat and water
2. radiation, water and oxygen
3. water, heat and oxygen
4. radiation, pressure and water
The three primary sources of the Earth's heat are:
1. residual heat from the Earth's formation, plate friction, and radioactivity
2. radioactivity, radiation absorbtion, and plate friction
3. residual heat from the Earth's formation, plate friction, and the geothermal gradient
4. volcanic eruption, radioactivity, and plate friction
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Temperatures in the Earth increase with depth at a rate referred to as the ______________
_________________.
True or False? The presence of water makes rocks easier to melt.
A ____________ is an intrusive igneous body formed from magma that cooled underground.
Unmelted rocks carried within magma are called ________________.
Country rock is:
1. rock located on the surface of the Earth
2. any common rock
3. preexisting rock into which magma intrudes
4. all rock that is assimilated into a magma flow
True or False? Gabbros are the most abundant igneous rocks and also the most variable.
True or False? Mid-ocean ridge basalts account for 65% of the Earth's surface area.
1. Which of the following is not part of the definition of a mineral?
1. naturally occurring
2. definite (characteristic) chemical composition
3. two or more chemical elements
4. crystalline solid
5. All of the above are in the definition of a mineral.
2. An atom that has gained electrons is called a(n) ____________ and has a ______________ charge.
1. cation; positive
2. cation; negative
3. anion; positive
4. anion; negative
5. isotope; neutral
3. The most common rock forming minerals belong to the _____________ group.
1. carbonate
2. silicate
3. phosphate
4. oxide
5. native element
4. Olivine is a ______________ silicate mineral that is most abundant in the Earth's ______________.
1. framework; mantle
2. framework; crust
3. sheet; crust
4. sheet; mantle
5. island; mantle
5. Carbonate minerals are most commonly found in _____________ rocks.
1. intrusive igneous
2. extrusive igneous
3. metamorphosed igneous
4. clastic sedimentary
5. chemical or biochemical sedimentary
6. In the mica minerals, (SiO4) tetrahedra are arranged in _____________.
1. single chains
2. double chains
3. sheets
4. frameworks
5. isolated pairs
7. ________ is a coarse-grained, mafic rock.
1. Granite
2. Obsidian
3. Basalt
4. Gabbro
5. None of the above
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8. A granite is a igneous rock of ___________ composition that underwent __________ cooling.
1. felsic; fast
2. felsic; slow
3. mafic; slow
4. mafic; fast
5. intermediate; slow
9. Which of the following igneous rock textures results from initial slow cooling followed by subsequent
rapid cooling?
1. coarse-grained (phaneritic)
2. fine-grained (aphanitic)
3. pegmatitc
4. porphyritic
5. vesicular
10. Minerals near the top of Bowen's Reaction Series crystallize at __________ temperatures and are most
common in _______________ igneous rocks.
1. high; felsic
2. low; felsic
3. intermediate; intermediate
4. high; mafic
5. low; mafic
In addition, here is a list of some topics that you should understand:
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Identify three types of chemical bonds. How are electrons shared in each of the bond types you
identified? What physical properties are associated with each bond type?
How are the silicate minerals classified according to their structure? Describe physical properties of two
minerals that reflect this internal atomic structure.
Diagram the rock cycle. What are the three major rock types and how does each form? Describe the
processes that are intermediate between the rock types (i.e., the interactions within the cycle).
What are the three ways to melt the mantle (to form a basaltic magma)? At which type of plate tectonic
setting does each of these occur? How do silicate magmas behave differently than water/ice with
regard to crystallization/melting behavior?
Learn the Big Chart. Live the Big Chart. Love the Big Chart.
How are the igneous rocks classified? Explain the relation between crystal size and cooling history in
igneous rocks.
Illustrate Bowen's Reaction Series with a labeled diagram. Include all relevant minerals and indicate
approximate temperatures of crystallization.
Ig_Rk_SG
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