Geology Ch. 8 Test

Slate and schist are both derived by metamorphism of shales and mudstones. This means that when shales and mudstones undergo metamorphic processes such as heat and pressure, they can transform into slate or schist. Therefore, the statement that slate and schist are both derived by metamorphism of shales and mudstones is true.

Calcite is indeed the main mineral constituent of both limestone and marble. Limestone is a sedimentary rock primarily composed of calcite, while marble is a metamorphic rock that forms from the recrystallization of limestone. Therefore, it is correct to say that calcite is the main mineral constituent of both limestone and marble.

The statement is true because these three factors - elevated temperature, elevated pressure, and the chemical action of hot fluids - are indeed involved in the process of metamorphism. Metamorphism refers to the transformation of rocks due to changes in these factors over time. Elevated temperature and pressure cause the minerals in rocks to recrystallize and rearrange their structure, resulting in the formation of new minerals and textures. The chemical action of hot fluids can also contribute to the alteration of rocks by introducing new elements and facilitating chemical reactions. Therefore, all three factors play a crucial role in the metamorphic process.

During metamorphism, solid mineral grains undergo changes in their texture, composition, and structure due to high temperature and pressure. However, in some cases, the metamorphic process can be facilitated by the presence of hot fluids or partial melting. These fluids can aid in the movement and recrystallization of minerals, leading to further changes in the rock. Therefore, it is true that small amounts of hot fluids or partial melting can play a role in the metamorphic process.

Partial melting is indeed an important process in the formation of migmatites. Migmatites are rocks that have undergone both partial melting and solidification. During partial melting, certain minerals within the rock melt at high temperatures, while others remain solid. This process leads to the formation of a partially molten rock, which then cools and solidifies to form a migmatite. Therefore, the statement "Partial melting is an important process in the formation of migmatites" is true.

The given statement is true because rock cleavage or slaty cleavage in slates is indeed largely a consequence of abundant, parallel-aligned, very fine-grained mica flakes in the rock. This alignment and arrangement of the mica flakes create a distinct parallel cleavage plane in the rock, which allows it to easily split into thin, flat sheets or slabs. This characteristic is what gives slates their characteristic ability to be easily split into thin layers and makes them suitable for use as roofing material or decorative purposes.

High-grade, regional metamorphism refers to intense heat and pressure that occur over large areas, such as during mountain-building processes. This type of metamorphism leads to significant changes in the textures and mineral compositions of rocks. The high temperatures and pressures cause minerals to recrystallize and form new minerals, resulting in the development of distinct textures and mineral assemblages. These changes are often visible and can be used to identify and classify metamorphic rocks. Therefore, the statement that high-grade, regional metamorphism produces significant and recognizable changes in the textures and mineral compositions of rocks is true.

Muscovite, biotite, and chlorite are indeed common minerals found in phyllites and schists. Phyllites and schists are both metamorphic rocks that have undergone intense heat and pressure, causing the minerals within them to recrystallize and rearrange. Muscovite, biotite, and chlorite are all common minerals that form during this process and are often found in these types of rocks. Therefore, the statement is true.

During episodes of mountain building, intense pressure and heat cause the rocks to undergo metamorphism, resulting in the formation of metamorphic rocks. These rocks often exhibit textural characteristics that indicate the presence of shearing stress and deformation, such as foliation and banding. This is because the intense forces and movement associated with mountain building can cause the minerals within the rocks to align and reorganize, creating these distinctive textures. Therefore, the statement that metamorphic rocks formed during episodes of mountain building typically show textural characteristics indicative of shearing stress and deformation is true.

Talc and graphite are indeed very soft minerals found in some schists. Talc is known for its softness and is commonly used in cosmetic products. Graphite, on the other hand, is a form of carbon that is also very soft and is used in pencils. Both minerals can be easily scratched or marked, confirming that the statement is true.

Gneisses are metamorphic rocks that are formed from the recrystallization of pre-existing rocks under high pressure and temperature conditions. These rocks often exhibit distinct layers or bands of different minerals, known as foliation. Due to the intense pressure and folding during their formation, these layers can become complexly folded, resulting in a characteristic pattern of folds within the gneiss. Therefore, the statement that the distinctive layers or bands of different minerals in gneisses may be complexly folded is true.

Marble forms from the metamorphism of limestone or dolostone. During metamorphism, the heat and pressure cause the minerals in limestone or dolostone to recrystallize, resulting in the formation of marble. This process also causes the original sedimentary textures and structures to be destroyed, and the rock becomes more compact and dense. Marble is known for its characteristic smooth texture, variety of colors, and ability to take a high polish, making it a popular material for sculptures, building facades, and countertops.

Marble and quartzite are two metamorphic rocks that are composed predominantly of single minerals. Marble is primarily made up of the mineral calcite, while quartzite is composed mainly of the mineral quartz. Both rocks undergo metamorphism, which causes the minerals within them to recrystallize and form a solid, interlocking structure. This results in the formation of rocks that are predominantly made up of a single mineral.

Amphibolite forms through regional metamorphism of volcanic rocks such as andesite and basalt. This process involves the transformation of existing rocks under high temperature and pressure conditions over a large area. As the volcanic rocks are subjected to these intense conditions, their mineral composition and texture change, resulting in the formation of amphibolite. This rock is characterized by the presence of hornblende and plagioclase minerals, which are indicative of its metamorphic origin. The other options listed do not involve the specific conditions required for the formation of amphibolite.

Foliation is the correct answer because it refers to the strong, parallel alignment of coarse mica flakes and/or different mineral bands in a metamorphic rock. This alignment occurs due to the intense pressure and heat during the rock's formation, causing the minerals to align in a specific direction. Foliation is a characteristic feature of metamorphic rocks and helps to distinguish them from other types of rocks.

Phyllite is a foliated metamorphic rock that is texturally intermediate between slate and schist. It is characterized by its fine-grained texture and a glossy sheen caused by the alignment of its microscopic mica minerals. Phyllite forms from the low-grade metamorphism of shale or slate, and its mineral composition includes primarily mica, quartz, and chlorite. It exhibits a higher degree of metamorphism than slate but is not as highly metamorphosed as schist.

Micas are the most visual aspect of foliated metamorphic rocks because they have a platy and parallel structure. This means that the mineral grains of micas are flat and aligned in parallel layers, giving the rock a characteristic foliated texture. Micas are also known for their shiny appearance and ability to split into thin sheets, which further enhances their visibility in metamorphic rocks.

Granitic gneiss is characterized by the segregation of light- and dark-colored minerals into thin layers or bands. This rock type forms through the metamorphism of granite, where the minerals within the granite recrystallize and align themselves into distinct layers. The light-colored minerals, such as quartz and feldspar, form the lighter bands, while the dark-colored minerals, such as biotite and amphibole, form the darker bands. This layering or banding gives granitic gneiss its characteristic appearance and distinguishes it from other rock types such as garnet hornfels, slate, and quartzite.

The major source of heat for contact metamorphism is heat from a nearby magma body. When magma intrudes into the surrounding rocks, it releases a significant amount of heat, causing the rocks to undergo metamorphic changes. This heat is responsible for altering the mineralogy and texture of the rocks in contact with the magma, leading to the formation of new minerals and the recrystallization of existing ones.

The term that describes the zone of contact metamorphism surrounding an intrusive magma body is aureole. This term refers to the area where the surrounding rocks are altered due to the heat and fluids released by the magma as it intrudes into the pre-existing rock. This metamorphism leads to the formation of new minerals and the recrystallization of existing ones, resulting in distinct changes in the rock composition and structure within the aureole.

Quartzite is typically formed by metamorphism of a sandstone. During the metamorphic process, the sandstone undergoes intense heat and pressure, causing the grains of sand to recrystallize and fuse together, forming a hard and durable rock known as quartzite. This process also leads to the removal of any original sedimentary features, resulting in a rock with a smooth and granular texture. Therefore, quartzite is the correct answer for this question.

Blueschists are a type of high-pressure metamorphic rock formed deep within the Earth's crust. They are not likely to be genetically associated with the impact of an asteroid or large meteorite because their formation process is unrelated to such events. Tektites, coesite, and impact craters, on the other hand, are directly linked to the impact of an asteroid or large meteorite and can be used as evidence of such an event.

The correct answer is slate, phyllite, schist. This is because in the process of metamorphism, rocks undergo changes in their mineral composition and texture. Slate is the lowest grade of metamorphic rock, with fine-grained texture and low-grade metamorphism. Phyllite is the next grade, with slightly larger grain size and higher grade of metamorphism. Schist is the highest grade, with even larger grain size and more advanced metamorphism. Therefore, the correct order is slate, phyllite, schist.

Migmatite would exhibit visible, textural evidence of having undergone some partial melting. Migmatite is a rock that has undergone both melting and solidification processes, resulting in a mixture of igneous and metamorphic features. It typically displays a banded appearance with light-colored, melted rock (magma) injections, known as leucosomes, within a darker, solidified matrix, known as melanosome. This distinctive texture is a clear indication of partial melting and subsequent recrystallization.

Contact metamorphism occurs when rocks come into contact with a nearby magma body, resulting in heat being transferred from the magma to the surrounding rocks. The pressures involved in contact metamorphism are relatively low, and the rocks undergoing metamorphism are typically located in the upper part of the Earth's crust. This process does not involve shearing or mechanical movements along faults.

Fault movements at shallow depths would exhibit sheared and mechanically fragmented rocks because when rocks experience faulting, they are subjected to intense stress and strain. This can result in the rocks breaking and sliding past each other along the fault plane, leading to shearing and fragmentation. The shallow depth of the fault movements implies that the rocks are not subjected to the high temperatures and pressures associated with deep-seated regional metamorphism or heating near a pluton, which are more likely to cause recrystallization and alteration rather than mechanical fragmentation. Regional metamorphism of pyroclastic volcanic rocks may lead to changes in mineral composition and texture, but not necessarily to shearing and fragmentation.

Chemically active fluids during metamorphism aid in the movement of dissolved silicate constituents and facilitate the growth of mineral grains. These fluids help to transport and distribute the dissolved minerals, allowing them to recrystallize and form new mineral grains. This process is essential for the development of metamorphic textures and the transformation of the rock. The fluids also play a role in chemical reactions, promoting the exchange of elements and the formation of new minerals.

Slate is a low-grade metamorphic rock that is composed of extremely fine-sized mica and other mineral grains. It typically exhibits well-developed rock cleavage, which refers to the tendency of the rock to split along parallel planes. This cleavage is a result of the alignment of the mica and other mineral grains during the metamorphic process. Schist, hornfels, and quartzite are also metamorphic rocks, but they do not typically exhibit the same level of well-developed rock cleavage as slate.

Marble is the correct answer because it is a metamorphic rock composed mainly of calcite or dolomite minerals, which have the ability to neutralize acidic waters. When acidic mine waters come into contact with marble, the calcite or dolomite minerals in the rock react with the acid, causing the pH of the water to increase and become more neutral. This makes marble an effective choice for neutralizing acidic mine waters.

Slate is a fine-grained metamorphic rock that forms from shales and mudstones. It is characterized by its rock cleavage, which means it can be easily split into thin sheets. Sedimentary features may also be visible in slate. However, slate does not have abundant, coarse-grained mica. Mica is a common mineral found in other types of rocks like granite, but it is not typically present in large quantities in slate.

Regional metamorphism is most likely to occur at great depths in the crust where two continents are colliding. This is because the collision of two continents causes intense pressure and heat, which leads to the formation of regional metamorphic rocks. In this setting, the rocks undergo significant changes in mineral composition and texture due to the high temperatures and pressures involved. The other options, such as shallow depths below an oceanic ridge or rift zone, along major transform faults in the continental crust, or beneath the seafloor where water pressures are immense, do not typically generate the same level of pressure and heat required for regional metamorphism.

Blueschist forms at high pressures but low temperatures during the subduction of oceanic crust and sediments. This metamorphic rock is characterized by its blue color and contains minerals such as glaucophane and lawsonite. The high pressure conditions cause the mineral grains to align in a specific orientation, giving blueschist its distinctive foliated texture. The moderately low temperatures prevent the rock from fully recrystallizing, resulting in a unique combination of mineral composition and texture.

Schist forms at the highest grade of regional metamorphism because it is a medium to coarse-grained metamorphic rock that has undergone intense heat and pressure. It exhibits foliation, which is a characteristic of high-grade metamorphic rocks. Hornfels, slate, and phyllite are formed at lower grades of metamorphism and do not exhibit the same level of metamorphic changes as schist.

During the metamorphism of limestone to marble, the major change that occurs is that the calcite grains in the limestone grow larger and increase in size. This process is known as recrystallization, where the existing calcite crystals rearrange and merge together, resulting in larger grains. This transformation gives marble its characteristic crystalline texture and increased hardness compared to limestone.

Hornfels is a nonfoliated rock that is formed through contact metamorphism of a shale or mudstone. Contact metamorphism occurs when rocks come into contact with hot magma or lava, causing the minerals in the rocks to recrystallize and form new minerals. In the case of hornfels, the high temperatures from the contact with the magma or lava cause the clay minerals in the shale or mudstone to recrystallize into a dense, fine-grained rock with no visible foliation. This process results in the formation of hornfels.

Tektites are glassy objects that are formed when meteorites impact the Earth's surface. The high temperatures generated during these impacts cause the surrounding rocks to melt and form tektites. Therefore, the correct answer is high temperatures associated with meteorite impacts.

Schistosity is the correct answer because it refers to the parallel alignment of abundant, coarse-grained mica flakes in a metamorphic rock. This alignment creates a foliation that is characteristic of schist rocks. Gneissic banding refers to alternating layers of light and dark minerals, slaty cleavage refers to the ability of a rock to split into thin sheets, and phyllitic structure refers to a fine-grained foliation resulting from low-grade metamorphism.

The presence of graphite in the schist suggests that the pre-metamorphic rock was a shale or mudstone containing organic matter. Graphite is a form of carbon that is commonly found in organic-rich rocks such as shale and mudstone. Therefore, it is justified to conclude that the pre-metamorphic rock in this case was a shale or mudstone with organic matter.

Amphibolites do not have gneissic textures and do not form by regional metamorphism of granites and rhyolites. Instead, they are formed by the metamorphism of basaltic rocks.

At high pressures and elevated temperatures of regional metamorphism, silicate rocks are actually more prone to flowage and deformation. This is because the increase in temperature and pressure causes the minerals in the rocks to become more ductile, allowing them to deform more easily. Therefore, the statement that silicate rocks are more resistant to flowage and deformation at high temperatures and pressures is false.

Foliated metamorphic rocks are not composed largely of equidimensional grains of minerals such as quartz and calcite. In fact, foliated metamorphic rocks have a layered or banded appearance due to the alignment of minerals in parallel planes or bands. These rocks typically contain elongated or platy minerals such as mica or chlorite. Therefore, the statement is false.

Hornfels are metamorphic rocks that are produced at great depths and high temperatures associated with contact metamorphism, not regional metamorphism.

The statement is false because quartzites and metaconglomerates are not formed along faults by intensive fracturing and fragmentation of conglomerate beds and quartz veins. Quartzites are formed through the metamorphism of quartz-rich sandstones, while metaconglomerates are formed through the metamorphism of conglomerates. Faulting and fracturing can occur in the formation of these rocks, but they are not the primary processes involved.