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Where Does Obsidian Form?
Obsidian is usually an extrusive rock – one that solidifies above Earth’s surface. However, it can form in a variety of cooling environments:
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What is Obsidian?
Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. It is an amorphous material known as a “mineraloid.” The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture (see photo).
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Uses of Granite
Granite is the rock most often quarried as a “dimension stone” (a natural rock material that will be cut into blocks or slabs of specific length, width, and thickness). Granite is hard enough to resist abrasion, strong enough to bear significant weight, inert enough to resist weathering, and it accepts a brilliant polish. These characteristics…
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When “Granite” Is Inadequate
So, the name “granite” is a name used for igneous rocks that are composed of orthoclase feldspar, quartz, plagioclase feldspar, micas, and amphiboles that are present in crystals large enough to be visible with the unaided eye. That name isn’t specific enough for some purposes and for some people. Special names are used for granitic rocks based…
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Multiple Definitions of Granite
The word “granite” is used in a variety of ways by different people. A simple definition is used in introductory geology or earth science courses. A more precise definition is used by petrologists (geologists who specialize in the study of rocks). And, the definition of granite expands wildly when used in the crushed stone and dimension stone…
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Granite in the Continental Crust
Introductory geology textbooks report that granite is the most abundant rock in the continental crust. At the surface, granite is exposed in the cores of many mountain ranges, within large areas known as “batholiths,” and in the core areas of continents known as “shields.” The large mineral crystals in granite are evidence that it cooled…
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The Best-Known Igneous Rock
Granite is the best-known igneous rock. Many people recognize granite because it is the most common igneous rock found at Earth’s surface and because granite is used to make many objects that they encounter in daily life. These include countertops, floor tiles, paving stone, curbing, stair treads, building veneer, and cemetery monuments. Granite is used…
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What is Granite?
Granite is a light-colored igneous rock with grains large enough to be visible with the unaided eye. It forms from the slow crystallization of magma below Earth’s surface. Granite is composed mainly of quartz and feldspar with minor amounts of mica, amphiboles, and other minerals. This mineral composition usually gives granite a red, pink, gray, or white color with dark mineral grains visible…
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Conglomerate on Mars
In September 2012, NASA’s Mars rover Curiosity discovered an outcrop of conglomerate exposed on the surface of Mars. The rounded clasts within the conglomerate provide evidence that a stream or a beach had moved the rocks and tumbled them into rounded pebbles. This conglomerate is one of the most convincing evidences that water once flowed…
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Puddingstone Conglomerate
Puddingstone is a nonscientific name for a conglomerate made up of clasts that contrast sharply with the color of the rock’s matrix. People in what is today the United Kingdom were the first to use the name. They claim that the rocks reminded them of a “plum pudding”. Puddingstones are found in many parts of the world. We…