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How Does Gneiss Form?
Gneiss usually forms by regional metamorphism at convergent plate boundaries. It is a high-grade metamorphic rock in which mineral grains recrystallized under intense heat and pressure. This alteration increased the size of the mineral grains and segregated them into bands, a transformation which made the rock and its minerals more stable in their metamorphic environment. Gneiss…
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What Is Gneiss?
Gneiss is a foliated metamorphic rock identified by its bands and lenses of varying mineral composition. Some of these bands (or lenses) contain granular minerals that are bound together in an interlocking texture. Other bands contain platy or elongated minerals that show a preferred orientation that parallels the overall banding in the rock. It is this banded appearance and texture…
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What are the Uses of Coal?
Electricity production is the primary use of coal in the United States. Most of the coal mined in the United States is transported to a power plant, crushed to a very small particle size, and burned. Heat from the burning coal is used to produce steam, which turns a generator to produce electricity. Most of the…
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What is Coal “Rank”?
Plant debris is a fragile material compared to the mineral materials that make up other rocks. As plant debris is exposed to the heat and pressure of burial, it changes in composition and properties. The “rank” of a coal is a measure of how much change has occurred. Sometimes the term “organic metamorphism” is used…
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How Does Coal Form?
Coal forms from the accumulation of plant debris, usually in a swamp environment. When a plant dies and falls into the swamp, the standing water of the swamp protects it from decay. Swamp waters are usually deficient in oxygen, which would react with the plant debris and cause it to decay. This lack of oxygen…
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Anthracite
The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter. What is Coal? Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment.…
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Uses of Amphibolite
Amphibolite has a variety of uses in the construction industry. It is harder than limestone and heavier than granite. These properties make it desirable for certain uses. Amphibolite is quarried and crushed for use as an aggregate in highway construction and as a ballast stone in railroad construction. It is also quarried and cut for use as a…
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How Does Amphibolite Form?
Amphibolite is a rock of convergent plate boundaries where heat and pressure cause regional metamorphism. It can be produced through the metamorphism of mafic igneous rocks such as basalt and gabbro, or from the metamorphism of clay-rich sedimentary rocks such as marl or graywacke. The metamorphism sometimes flattens and elongates the mineral grains to produce a schistose texture.
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What is Amphibolite?
Amphibolite is a coarse-grained metamorphic rock that is composed mainly of green, brown, or black amphibole minerals and plagioclase feldspar. The amphiboles are usually members of the hornblende group. It can also contain minor amounts of other metamorphic minerals such as biotite, epidote, garnet, wollastonite, andalusite, staurolite, kyanite, and sillimanite. Quartz, magnetite, and calcite can also be present in small amounts.
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Dacite on Mars
In 2002, NASA’s THEMIS spacecraft began orbiting Mars, scanning the surface of the planet with a thermal emission imaging system. Instruments on the spacecraft had the ability to characterize the mineralogy of rock units exposed on the surface of Mars. Their goals were to identify the rock types on the surface of Mars and map their geographic…