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Chalk is so common in Cretaceous marine beds that the Cretaceous Period was named for these deposits. The name Cretaceous was derived from Latin creta, meaning chalk. [10] Some deposits of chalk were formed after the Cretaceous. [11] The Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period.
The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Upper Cretaceous limestone succession in southern and eastern England. The same or similar rock sequences occur across the wider northwest European chalk 'province'.
Limestone is commonly white to gray in color. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone an off-white to yellow to red color. The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk.
Chalk mining is the extraction of chalk from underground and above ground deposits by mining. [1] Mined chalk is used mostly to make cement and bricks . Chalk mining was widespread in Britain in the 19th century because of the large amount of construction underway (and the Industrial Revolution ). [ 2 ]
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, [1] [2] categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start fires .
Niobrara Chalk was weathered and opalized in the Valentine phase of the Ogallala Formation. The Niobrara Formation / ˌ n aɪ. ə ˈ b r ær ə /, also called the Niobrara Chalk, is a geologic formation in North America that was deposited between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian stages of the Late ...
The Munsell color wheel prompted Binney & Smith to adopt a similar color wheel concept for Crayola crayons in 1930, using six principal hues (red, orange, yellow, green, blue, and violet) and six intermediate hues (red-orange, yellow-orange, yellow-green, blue-green, blue-violet, and red-violet), for a twelve-color wheel.
Chalk is a type of sedimentary rock, composed predominantly of calcium carbonate. Chalk may also refer to: The Chalk Group, a stratigraphic unit in northwest Europe. The Chalk country, a region of Discworld; Blackboard chalk and sidewalk chalk, a material used for writing and art, usually composed of calcium sulfate or calcium carbonate.