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Alibates Flint Quarries
In the area that is now the Texas panhandle, Native Americans discovered an area where weathered flint littered the ground. This flint was weathering out of a dolomite beneath the thin soil cover. These people discovered that fresh, unweathered flint of high quality could be obtained by digging down a few feet. From about 13,000 years ago…
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Flint Ridge Quarries, Ohio
One of the most important localities for flint in eastern North America is Flint Ridge in eastern Ohio. Native Americans discovered this deposit and produced flint from hundreds of small quarries along the ridge. This “Ohio Flint” occurred in distinctive colors and was treasured by Native Americans. They travelled hundreds of miles to collect it…
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The Preferred Tool-Making Material
Flint has been used by humans to make stone tools for at least two million years. [1] The conchoidal fracture of flint causes it to break into sharp-edged pieces. Early people recognized this property of flint and learned how to fashion it into knife blades, projectile points, scrapers, axes, drills, and other sharp tools. They…
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What is Flint?
Flint is a hard, tough chemical or biochemical sedimentary rock that breaks with a conchoidal fracture. It is a form of microcrystalline quartz that is typically called “chert” by geologists. Flint often forms as nodules in sedimentary rocks such as chalk and marine limestones. The nodules can be dispersed randomly throughout the rock unit but are often concentrated in distinct layers. Some rock…
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Uses of Dolomite
Dolomite and limestone are used in similar ways. They are crushed and used as an aggregate in construction projects. They are kiln-fired in the manufacture of cement. They are cut into blocks and slabs for use as a dimension stone. They are calcined to produce lime. In some of these uses, dolomite is preferred. Its…
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Metamorphism of Dolomite
Dolomite behaves like limestone when it is subjected to heat and pressure. It begins to recrystallize as the temperature rises. As this occurs, the size of the dolomite crystals in the rock increases, and the rock develops a distinctly crystalline appearance. If you examine the photo of granular dolomite, you will see that the rock…
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“Dolomite Rock” and “Dolostone”
Some geologists are uncomfortable using the word “dolomite” for both a mineral and a rock of the same composition. They instead prefer using “dolomite rock” or “dolostone” when speaking of the sedimentary rock and “dolomite” when speaking of the mineral. Although these terms simplify communication and improve accuracy, many geologists continue to use the word “dolomite” for both the mineral…
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Identification in the Field and Classroom
Dolomite is slightly harder than limestone. Dolomite has a Mohs hardness of 3.5 to 4, and limestone (composed of the mineral calcite) has a hardness of 3. Dolomite is slightly less soluble in dilute hydrochloric acid. Calcite will effervesce vigorously in contact with cold, dilute (5%) hydrochloric acid, while dolomite produces a very weak effervescence. These differences…
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Dolomitization
Dolomite is very common in the rock record, but the mineral dolomite is rarely observed forming in sedimentary environments. For this reason it is believed that most dolomites form when lime muds or limestones are modified by postdepositional chemical change. Dolomite originates in the same sedimentary environments as limestone – warm, shallow, marine environments where…
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What is Dolomite?
Dolomite, also known as “dolostone” and “dolomite rock,” is a sedimentary rock composed primarily of the mineral dolomite, CaMg(CO3)2. Dolomite is found in sedimentary basins worldwide. It is thought to form by the postdepositional alteration of lime mud and limestone by magnesium-rich groundwater. Dolomite and limestone are very similar rocks. They share the same color ranges of white-to-gray and white-to-light…