Question

Each of the following statements describes one or more characteristics of a particular metamorphic rock. For each statement, identify the metamorphic rock being described: a. calcite rich and nonfoliated b. loosely coherent and composed of broken fragments that formed along a fault zone C. represents a grade of metamorphism between slate and schist d. composed of tiny chlorite and mica grains and displays excellent rock cleavage e. foliated and composed predominately of platy materials f. composed of alternating bands of light and dark silicate minerals g. hard and nonfoliated, often produced by contact metamorphism

Short answer

a. Marble, b. Fault breccia, c. Phyllite, d. Slate, e. Schist, f. Gneiss, g. Quartzite.

Step-by-step solution

Analyzing Statement (a)

The statement "calcite rich and nonfoliated" describes a rock that is primarily made of calcite and does not display a layered or banded appearance known as foliation. The rock that fits this description is marble, which is a metamorphic rock resulting from the metamorphism of limestone.

Analyzing Statement (b)

The statement "loosely coherent and composed of broken fragments that formed along a fault zone" refers to a rock that is formed from broken pieces and is not strongly cemented together. This type of metamorphic rock is known as fault breccia.

Analyzing Statement (c)

The statement "represents a grade of metamorphism between slate and schist" indicates a rock that has undergone more metamorphism than slate but less than schist. The rock that fits this grade is phyllite, characterized by a slight sheen due to microscopic mica flakes.

Analyzing Statement (d)

The statement "composed of tiny chlorite and mica grains and displays excellent rock cleavage" describes a rock known for its fine grain size and ability to split along smooth planes. This description fits slate, which is a low-grade metamorphic rock.

Analyzing Statement (e)

The statement "foliated and composed predominately of platy materials" suggests a metamorphic rock that has a layered structure due to the alignment of flat mineral grains. Schist is the rock that fits this description, known for its foliated appearance due to the abundance of mica.

Analyzing Statement (f)

The statement "composed of alternating bands of light and dark silicate minerals" describes a rock that exhibits banding or a striped appearance. Gneiss is a metamorphic rock recognized by its formation of light and dark mineral layers.

Analyzing Statement (g)

The statement "hard and nonfoliated, often produced by contact metamorphism" refers to rocks that are dense, resistant to weathering, and lack any evident banding. Quartzite is frequently produced through the contact metamorphism of quartz-rich sandstone, fitting this description.

Key concepts

Marble

Marble is a well-known metamorphic rock that originates from limestone. It is primarily composed of calcite, a mineral that gives marble its characteristic richness. Its formation process involves the metamorphism of limestone under conditions of high pressure and temperature. During this transformation, the calcite crystals in the limestone recrystallize, resulting in a denser rock. One of the key features of marble is that it is nonfoliated, meaning it does not have a layered or banded appearance. This lack of foliation makes marble ideal for sculpture and construction, as it can be easily carved into intricate shapes.
Marble can be found in a variety of colors, ranging from the classic white to shades of gray, pink, and green, often with swirls of different hues. This color variation is due to impurities present in the original limestone. Not only is marble appreciated for its aesthetic qualities, but it is also valued for its durability and resistance to weathering, making it a popular choice for both interior and exterior applications.

Phyllite

Phyllite is a metamorphic rock that sits between slate and schist in the metamorphic grade spectrum. It forms under relatively low to intermediate levels of heat and pressure, causing the development of fine-grained mica flakes. These give phyllite its characteristic sheen or silky appearance, distinguishing it from slate.
Phyllite's rock surfaces often possess a wavy or crinkled appearance due to the alignment of its mineral grains. Although its cleavage is typically not as prominent as that of slate, phyllite still displays some ability to split along planes, making it useful for decorative stone applications.

• Intermediate grade metamorphism
• Silky sheen from mica flakes
• Wavy foliation

Phyllite can exhibit a variety of colors, including shades of gray, green, red, or purple, which depend on the composition of the original material and the metamorphic conditions.

Slate

Slate is a fine-grained, foliated metamorphic rock that is derived from an original shale-type sedimentary rock composed of clay or volcanic ash. It forms under relatively low-grade metamorphic conditions involving heat and pressure that lead to the parallel alignment of tiny chlorite and mica grains.
This alignment causes slate to exhibit excellent rock cleavage, which allows it to split into thin, durable sheets. These properties make slate an outstanding material for roofing tiles, flooring, and flagstones. Because of its dense and uniform composition, slate tends to weather very slowly, maintaining its appearance over time.

• Low-grade metamorphism
• Excellent cleavage
• Commonly used in construction

Slate commonly appears in various shades of gray, but can also be found in reds, greens, and purples, depending on its mineral content.

Schist

Schist is known for its distinct foliated texture, characterized by large, conspicuous mineral grains that are visible to the naked eye. This is a result of its formation under higher temperature and pressure conditions compared to slate and phyllite. Schist is primarily composed of platy minerals like mica, giving it a shiny appearance.
The foliation in schist occurs because the minerals, predominantly aligned parallel to each other, contribute to the rock's distinct layered structure. This alignment is often so pronounced that schist can sometimes be mistaken for having a true banded appearance.

• High content of platy minerals
• Distinct foliation
• Typically used in decorative and architectural applications

Due to its mineral composition, schist varies widely in color and texture, depending on the types of minerals present during metamorphism.

Gneiss

Gneiss is easily recognized by its distinct banded appearance, characterized by alternating layers of light and dark silicate minerals. This metamorphic rock forms under even higher temperatures and pressures than schist, resulting in a more fully recrystallized structure.
The banding in gneiss, unlike foliation, results from the segregation of mineral types, which may include feldspar, quartz, and mica. This distinctive appearance makes gneiss particularly attractive and useful in architectural applications.

• High-grade metamorphism
• Banding from mineral segregation
• Applications in construction and design

Gneiss is known for its strength and durability, often used in flooring and curbing, offering both aesthetic and functional benefits.

Quartzite

Quartzite is a dense, hard metamorphic rock that emerges from the metamorphism of quartz-rich sandstone. It is nonfoliated, meaning it lacks the layering seen in rocks like schist or gneiss. This characteristic makes quartzite very resistant to physical weathering and chemical erosion.
The transformation from sandstone to quartzite involves the recrystallization of quartz grains, which become tightly interlocked, contributing to the rock's robustness. Due to its vitreous luster and variety in colors, ranging from white to shades of pink and red, quartzite is highly prized for use in construction and ornamental stone applications.

• Produced by the metamorphism of sandstone
• Nonfoliated texture
• High resistance to weathering

Quartzite's combination of beauty and strength makes it a preferred material for countertops, roofing tiles, and as a dimension stone.