Geology exam 2
The size of the volcanic fragments
What differentiates welded tuff from volcanic breccia?
Pyroxene
What do the olivine crystals convert to as the temperature of magma cools?
Amphibole
What do the pyroxene crystals convert to as the temperature of magma cools?
Biotite
What do the pyroxene crystals convert to as the temperature of magma cools?
Batholith
What is the largest of all the plutons?
Granite
What is the most common igneous rock?
Fractional crystallization
What is the process by which a magma becomes progressively more felsic as it cools?
Ignimbrites
What are rocks formed when deposits of pyroclastic flows solidify?
Olivine
What is the very first crystal to form as magma begins to cool?
Welded tuff
What rock is formed from volcanic fragments classified as ash (sand grain) in size?
Scoria basalt
What rock is mafic in composition and vesicular in texture?
Granite
What rock is phaneritic in texture and composed of quartz, muscovite, and K+ feldspar?
Ferromagnesian silicates
What type of rocks are in the discontinuous branch of Bowen's reaction series?
Welded tuff or volcanic breccia
What rock can be any of the 3 compositions and but only pyroclastic in texture?
Peridotite
What rock composes the upper part of the earth's mantle?
Diorite
What rock is intermediate in composition and phaneritic in texture?
Basalt
What rock is mafic in composition and aphanitic in texture?
Gabbro
What rock is mafic in composition and phaneritic in texture?
Scoria
What rock is most often seen in rock gardens or in dry saunas because it is inexpensive and very lightweight?
Granite
Which rock could be classified as: a) a phaneritic rock. b) felsic in composition. c) could be found in a batholith. d) the coarse-grained equivalent of rhyolite.
Eyjafjallajokull
Which volcanoes eruption in 2010 caused almost all air traffic across Europe to be shut down?
Submerging them in cold mercury
How did Bowen cool the melted powdered mafic minerals in his experiments?
Basalt
What is the Rosetta stone made of?
Crater
What is the circular depression at the top of a volcano?
True
*T/F:* Magmatic rocks are classified according to their silica content.
Ash flows
What are ignimbrites generated by?
True
*T/F:* A factor that influences the chemical composition of magmas is melting and assimilation of some of the rock of the magma chamber walls.
True
*T/F:* A factor that influences the chemical composition of magmas is mixing of magmas brought together from different locations.
True
*T/F:* A factor that influences the chemical composition of magmas is only partial melting of the source rock.
True
*T/F:* Anything that can be aphanytic can be porphyritic.
True
*T/F:* As magma cools, the feldspar will become less calcium rich and become more sodium rich.
True; Erosion of soft exterior rocks has exposed the frozen lava that filled the vents at Devil's Tower and Shiprock.
*T/F:* Devil's Tower, Wyoming, and Shiprock, New Mexico, are landforms that exist because softer volcano exteriors erode faster than solidified lava in fissures and vents.
True
*T/F:* Factors that influence the chemical composition of magmas may include the chemical composition of the source rock.
False; Felsic magma is more viscous because the silicon tetrahedrons link up in chains, which at the microscopic level tangle and impede smooth flow.
*T/F:* Felsic magma is less viscous than mafic magma.
False; Igneous rocks are aphanitic if they're fine-grained, phaneritic if they're coarse-grained.
*T/F:* Igneous rocks are coarse-grained if they're intrusive.
False; They're called pyroclastic rocks
*T/F:* Igneous rocks formed of igneous debris blown out of a volcano are called pegmatites.
True
*T/F:* Intermediate rocks are often called "salt and pepper" rocks.
True
*T/F:* Intrusions are bodies of rock that have never been erupted.
True
*T/F:* Intrusions are classified by size.
True; Volcanic rocks, like basalt, andesite, and rhyolite, are fine-grained extrusive igneous rocks. Intrusive igneous rocks do solidify in the Earth but eventually are exposed by erosion.
*T/F:* Intrusive igneous rocks cool slowly and are coarse-grained.
False; Lava often travels no faster than several feet per hour, and most flows move no faster than about 30 km (18 mph); people can usually get out of the way.
*T/F:* Lava is the greatest volcanic hazard to human life because it travels so fast.
False; The rocks formed of mafic minerals would be basalt and gabbro.
*T/F:* Mafic minerals form rhyolite and granite.
False; The hotter the magma, the less viscous it is and the faster it flows.
*T/F:* Magma moves up toward Earth's surface more quickly as it cools and therefore becomes less viscous.
True
*T/F:* Obsidian appears to be black, but it actually translucent or smoky.
True
*T/F:* Olivine and quartz are never found in the same rocks.
False;
*T/F:* Pegmatite has a very glassy texture.
False; Pegmatite is a very coarse-grained rock (which means it has very large crystals); glassy means no crystalline structure.
*T/F:* Pegmatite has a very glassy texture.
False; Pegmatites have cooled quickly but are, surprisingly, very coarse-grained because they form in water-rich melts that allow atoms to move around quickly and develop large crystals.
*T/F:* Pegmatites have intruded at great depth and cooled very slowly.
False; Since it's on the left side of the solidus line, it is solid. The region to the right of the liquidus line represents molten rock. Between the two lines, the rock is a mixture of solid and melt.
*T/F:* Point A represents rock that's physical state is molten.
True; Pyroclastic flows move extremely fast (100 to 300 km/h) and are very hot (500 to 1000°C). No person, animal, or plant could survive if caught in the path of a pyroclastic flow.
*T/F:* Pyroclastic flows bring instant death to any life caught in them.
True
*T/F:* Quartz is very common in a rock with a felsic composition.
True; Earth's temperature increases with depth, so the deeper an intrusion is, the hotter its environment and the longer it takes for it to cool.
*T/F:* The deeper an igneous intrusion, the slower it cools.
False; fractional crystallization
*T/F:* The sequence of mineral production that takes place in a cooling magma, called Bowen's reaction series, is an example of the process called stoping.
True
*T/F:* There is a well ordered sequence to fractional crystalization and it always happens in the same sequence.
True; Tuff is composed of fine pieces (volcanic ash); breccia is composed of larger, angular pieces.
*T/F:* Tuff and breccia are both fragmental igneous rocks.
True
*T/F:* Volcanic ash deposits are often Rhyolite.
True; The presence of volatiles helps break chemical bonds, resulting in a lower melting temperature for the wet rock.
*T/F:* Wet igneous rock (rock that contains volatiles) melts at a lower temperature than does the dry version of that same rock.
True
*T/F:* You cannot identify individual crystals in an extrusive rock.
Felsic
-High-silica content -Acid type magma -Thick and viscous -Slow moving -Light color minerals form such as feldspar and quartz -Example: granite/rhyolite -Nonferromagnesian minerals -Mostly intrusive and continental rock
Mafic (Magnesium & Ferric)
-Low-silica content -Basic type magma -Hotter and more fluid -Fast moving -Dark color minerals form that are high in calcium (Ca), iron (Fe), and magnesium (Mg) so dark color rocks form -Ferromagnesian minerals -Mostly extrusive rock and the mantle
Rhyolite
A coarse-grained granite is most similar in mineral composition to what fine-grained rock type?
Composition
How are diorite, andesite, and scoria related?
Composition
How are gabbro, basalt, and scoria related?
Texture
How are granite, diorite, and gabbro related?
Composition
How are granite, rhyolite, pumice, and obsidian related?
Texture
How are pumice, obsidian, and scoria related?
Texture
How are rhyolite, andesite, and basalt related?
440 meters
How much did the summit of Mount St. Helens lower after its eruption in 1980?
K+ Feldspar, Muscovite, Quartz, and Sodium rich Plagioclase Feldspar
If a felsic rock is found, what minerals are expected to compose it?
Olivine, Pyroxene, Plagioclase Feldspars that are rich in Calcium
If a mafic rock is found, what minerals are expected to compose it?
A small amount of Pyroxene, Amphibole, a good bit of Biotite, and Plagioclase Feldspars that have a mix of Calcium and Sodium
If an intermediate rock is found, what minerals are expected to compose it?
Extrusive
In what type of magma would you find larger phenocryst with a fine grained ground mass?
Intrusive
In what type of magma would you find very large phenocryst with coarse-grained ground mass?
Extrusive; Pillow lava forms by extrusive flows at mid-ocean ridges, where seawater rapidly cools basaltic lava into pillow-shaped blobs.
Is pillow lava intrusive or extrusive?
No
Is volcanic glass a true mineral?
Porphyritic
Magma that has gone through the 2 stages of cooling?
A submarine volcano; Pillow lava is a low-silica-content, basaltic lava associated with underwater effusive eruptions.
Pillow lavas are evidence of what volcanic circumstance?
Plagioclase feldspars
These are feldspars that will contain calcium, sodium, or both - but NO potassium?
Ash
What are fragments that are smaller than a sand grain in size?
Vesicles
What are gas-bubble holes frozen into lava as it solidifies?
Batholiths
What are intrusive igneous structures?
Plutonic
What are intrusive rocks also called?
Earthquake activity, change in heat flow from the volcano's surface, bulges on the volcano's surface, increase in gas emissions and hydrothermal activities
What are some warning signs of a volcano's imminent eruption?
Volatiles
What are substances that have a tendency to evaporate and are stable as gases?
K+ Feldspar, Muscovite, and Quartz
What are the 3 final minerals that will form as the magma cools?
Lapilli
What are the pea sized volcanic fragments composed of glassy lava and scoria basalt?
Dormant
What are volcanoes called that have not erupted in hundreds to thousands of years, but have the potential to erupt again?
Most likely K+ Feldspar
What does pink coloring mean in a rock?
Nickle
What element does peridotite contain, making it toxic to plants?
Bowen's reaction series
What has a continuous track in which there's a progressive change from calcium-rich to sodium-rich plagioclase?
Bowen's reaction series
What has a discontinuous track in which each step yields a different class of silicate mineral?
Basaltic sill
What is a black, fine-grained tabular intrusion between two layers of horizontal sedimentary rock?
Pyroclastic flow or nuée ardent
What is a fast-moving avalanche of hot gases and volcanic pieces?
Phenocryst
What is a large crystal surrounded by a finer-grained igneous rock?
Fissure eruption
What is a single eruption that occurs in a linear pattern through an extremely elongated vent?
Lava dome
What is a steep feature called formed from the eruption of rhyolitic lava?
Xenolith
What is a stoped block called that does not melt entirely during assimilation, but rather becoming surrounded by new igneous rock?
Fissure
What is a vertical elongated crack that serves as a conduit?
Jokulhaup
What is a volcanic eruption under a glacier called?
Lahar
What is a volcanic mud-and-debris flow that resembles fluid concrete?
Krakatau, Indonesia, 1883
What is an example of a phreatomagmatic eruption?
Obsidian
What is an example of a rock with a glassy texture?
Pumice
What is an example of a rock with a vesicular texture?
Phreatomagmatic eruption
What is an explosive (pyroclastic) eruption involving the reaction of water with magma?
Fine-grained
What is another textural term for aphanitic?
Coarse-grained
What is another textural term for phaneritic?
Glassy texture or a volcanic glass
What is developed when magma cools so quickly that crystals do not have time to develop?
Vesicular
What is formed when magma has an excessive amount of dissolved gasses?
Depth of the magma below the earth's surface
What is least likely to cause variation of the original composition of magmas?
Batholith
What is light-colored granite, an intrusive, coarse-grained, igneous rock?
Ferromagnesian silicate
What is olivine classified as?
Olivine
What is peridotite mostly composed of?
Stoping
What is the process of magma assimilating wall rock as blocks of it break off and sink into the magma?
Assimilation
What is the process of magma in a magma chamber melting the surrounding wall rock and incorporating it into itself, thus altering the composition?
Tephra
What is the term for an unconsolidated accumulation of any size of pyroclastic grains?
Magma chamber
What is the underground zone where magma accumulates?
Pegmatite
What is the very coarse-grained igneous rock that contains crystals up to tens of centimeters across and forms in dike-shaped intrustions from water-rich melts?
Vent
What is the volcano's opening to Earth's surface called?
Pillow basalts; Pillow basalts are bulbous flows of molten basalt, low in silica, which cool and harden as they are expelled into seawater.
What kind of basalts are formed in a submarine environment?
Extrusive igneous rock
What kind of igneous rock is dark-colored, fine-grained basalt?
Quartz
What mineral forms at the very lowest temperature?
Mud flows
What normally forms volcanic breccias?
Iron and magnesium
What other two elements can be found in olivine?
Columnar jointing
What produces hexagonal columns in cooled near-surface lava flows?
Vesicular
What rock has a very rough surface but is very lightweight?
Obsidian
What rock is either felsic or intermediate in composition and glassy in texture?
Pumice
What rock is either felsic or intermediate in composition and vesicular in texture?
Rhyolite
What rock is felsic in composition and aphanitic in texture?
Granite
What rock is felsic in composition and phaneritic in texture?
Volcanic breccia
What rock is formed from volcanic fragments that are larger than sand grain (ash) in size?
Andesite
What rock is intermediate in composition and aphanitic in texture?
Peridotite
What rock is ultramafic in composition and phaneritic in texture?
Bowen's reaction series
What shows the sequence in which different silicate minerals form during the progressive cooling of a mafic melt?
Mt. St. Helens
What stratovolcano recently erupted in the United States, killing many people, partly because it first blew sideways and produced a monstrous landslide, sending tons of ash skyward and blasted more than 1,000 feet off the mountaintop?
Pyroclastic
What texture are volcanic breccias and welded tuffs?
Cool, felsic, gas-rich lava
What type of conditions will result in the most violent, explosive volcanic eruption?
Large crystals
What type of crystals do cooling intrusive magmas produce?
Calcium only
What type of feldspar is the first to form as magma begins to cool?
Phaneritic
What type of igneous rock texture has crystals that can be seen with the naked eye?
Rhyolite lava
What type of lava has more silica than basalt lava does, indicates the tendency for explosive activity, may freeze in the vent and emerge as a spine, and may form a lava dome above the vent?
Intrusive
What type of magma cools underground slowly?
Extrusive
What type of magma cools very quickly from a volcanic eruption?
Frothy, foamy, and very gas rich magma
What type of magma forms vesicular rocks?
Divergent
What type of plate boundary is Surtsey located along?
Coarse grained ground mass with a larger crystal
What type of rock textures will be formed from intrusive magma?
Fine grained ground mass with a smaller crystal
What type of rocks will be formed from extrusive magma?
Low viscosity
What type of viscosity of lava could build a shield cone, indicates an area that has little potential for explosive eruptions, is basalt, and has low silica content?
Bowen's reaction series
What was established by laboratory experiments in which mafic melt was quenched in mercury?
Granitic dike
What would be classified as a light-tan tabular intrusion that cuts vertically across layered country rock?
More felsic
When rock is *partially* melted, how does the composition change in relation to the original rock?
United States, Alaska
Where is the Redoubt volcano located that produced a giant, mushroom shaped cloud of ash that reached the stratosphere?
Shiprock, NM
Where is the most famous set of dikes located?
Continuous
Which branch of Bowen's reaction series gives different varieties of the SAME mineral?
Gabbro
Which mafic rock is felsic granite most similar to in *texture*?
Ultramafic
Which magma composition is usually very dark green?
Pyroclastic
Which magma rock texture is made from very hot and sticky ash?
Aphanitic
Which magma rock texture is too small to be seen with the naked eye?
Kilauea, Hawaii; Hawaii sits on a hot spot, far from any plate boundary.
Which volcanic feature is NOT related to plate-boundary magmatism?
Obsidian; arrowheads and spears
Which volcanic material is highly prized by native Americans because of its usefulness as weapons?
Krakatau
Which volcano eruption in 1883 shot so much volcanic ash into the atmosphere that it created spectacular sunsets around the world for years?
Vulcan
Who was the Roman god of fire?
