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Uses of Unakite
Unakite has a surprising range of uses: it is made into crushed stone used in highway construction, and it is cut and polished for use as a gem. Few rocks have such a diversity of uses. The uses of unakite are summarized below. Gem and Jewelry Use Unakite is often cut into cabochons, beads, and other shapes that will be…
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What Is Unakite?
Unakite is a pink and green metamorphic rock composed of pink orthoclase, green epidote, and colorless to milky quartz. These colors have helped Unakite become a popular lapidary material. Unakite forms when granite is altered by hydrothermal fluids, and plagioclase in the granite is transformed into epidote. Unakite is used as a construction material, an architectural stone, a lapidary rough, and a gem material.
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Many Types of Tuff
“Tuff” is a name that is used for a broad range of materials. The only requirement is that the materials are ejecta produced by a volcanic eruption. Tuff can contain fragments of dust-size particles to boulder-size particles and be composed of many different types of material. Mount St. Helens tephra: Photograph of an outcrop of stratified…
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Welded Tuff
Sometimes the ejecta is hot enough when it lands that the particles are soft and sticky. These materials “weld” together upon impact or upon compaction. The rock formed from this hot ejecta is known as a “welded tuff” – because the ejected particles are welded together. Some deposits might contain welded tuff near the vent…
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Tuff Rings
A “tuff ring” is a small volcanic cone of low relief that surrounds a shallow crater. These craters, known as maars, are formed by explosions caused by hot magma coming in contact with cold groundwater. The explosion blasts fragments of bedrock, tephra, and ash from the crater. The tuff ring forms as these ejected materials fall back to…
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What is Tuff?
Tuff is an igneous rock that forms from the products of an explosive volcanic eruption. In these eruptions, the volcano blasts rock, ash, magma and other materials from its vent. This ejecta travels through the air and falls back to Earth in the area surrounding the volcano. If the ejected material is compacted and cemented into a rock, that rock will be…
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Scoria Substitutes
Where scoria is not available, a lightweight aggregate can be produced by heating shale in a rotating kiln under controlled conditions. With the proper type of shale, the material will have the properties, appearance, and vesicles of scoria. It is sold under the name “expanded aggregate,” “expanded clay,” or “grow rocks” and used for the…
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Uses of Scoria
One of the main uses of scoria is in the production of lightweight aggregate. The scoria is crushed to desired sizes and sold for a variety of uses. Concrete made with scoria typically weighs about 100 pounds per cubic foot. This is a weight savings compared to concrete made with typical sand and gravel that…
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Not to be Confused with Pumice
A vesicular igneous rock that is very similar to scoria is pumice. There are a few differences that can be used to distinguish them. First is their color. Scoria is almost always black or dark gray to reddish brown, while pumice is almost always white to light gray to light tan. This color difference is a…
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The Beverage Bottle Analogy
Have you ever slowly opened a bottle that contains a carbonated beverage and watched the gas bubbles form on the walls of the bottle? Then as the seal on the bottle is broken, the bubbles grow larger and a hiss of gas escapes from the bottle, followed by a rush of foam. The depressurization and…