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Making Fire and Sharpening Steel
Chert is a very hard material that produces a spark when it is struck against steel. The heat from this spark can be used to start fires. A “flintlock” is an early firearm in which a charge of gunpowder is ignited by a flint hammer striking a metal plate (see photo). A variety of metamorphosed…
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Chert Used to Make Sharp Tools
Chert has very few uses today; however, it was a very important tool-making material in the past. Chert has two properties that made it especially useful: 1) it breaks with a conchoidal fracture to form very sharp edges, and, 2) it is very hard. The edges of broken chert are sharp and tend to retain…
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What Color is Chert?
Chert occurs in a wide variety of colors. Continuous color gradients exist between white and black or between cream and brown. Green, yellow, orange, and red cherts are also common. The darker colors often result from inclusions of mineral matter and organic matter. Abundant iron oxides in the chert can produce a red color. The…
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What is Chert’s Composition?
Chert is a microcrystalline silicon dioxide (SiO2). As chert nodules or concretions grow within a sediment mass, their growth can incorporate significant amounts of the surrounding sediment as inclusions. These inclusions can impart a distinctive color to the chert.
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How Does Chert Form?
Chert can form when microcrystals of silicon dioxide grow within soft sediments that will become limestone or chalk. In these sediments, enormous numbers of silicon dioxide microcrystals grow into irregularly-shaped nodules or concretions when dissolved silica is transported to the formation site by the movement of groundwater. If the nodules or concretions are numerous, they can grow large…
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What is Chert?
Chert is a sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). It occurs as nodules, concretionary masses, and as layered deposits. Chert breaks with a conchoidal fracture, often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting tools and weapons. “Chert” and “flint” are names…
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Another Definition of Marble
The name “marble” is used in a different way in the dimension stone trade. Any crystalline carbonate rock that has an ability to accept a polish is called “marble.” The name is sometimes used for other soft rocks such as travertine, verd antique, serpentine, and some limestones.
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Physical Properties and Uses of Marble
Marble occurs in large deposits that can be hundreds of feet thick and geographically extensive. This allows it to be economically mined on a large scale, with some mines and quarries producing millions of tons per year. Most marble is made into either crushed stone or dimension stone. Crushed stone is used as an aggregate in highways,…
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How Does Marble Form?
The transformation of limestone into marble usually occurs at convergent plate boundaries where large areas of Earth’s crust are exposed to the heat and pressure of regional metamorphism. Some marble also forms by contact metamorphism when a hot magma body heats adjacent limestone or dolostone. This process also occurs at convergent plate boundaries Before metamorphism, the calcite…
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Marble
What is Marble? Marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism. It is composed primarily of the mineral calcite (CaCO3) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite. Under the conditions of metamorphism, the calcite in the limestone recrystallizes to form a rock that is a mass…