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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 is now divided into a White Chalk Subgroup and a Grey Chalk Subgroup, both of which are further subdivided into formations.These modern divisions replace numerous earlier divisions, references to which occur widely on geological maps and in other geological literature.
Some chalk mines were extensively large, with passages up to 25 feet (7.6 m) high and 15 feet (4.6 m) wide, their passages taking the form of a Norman arch. Because of chalk's softness, picks and shovels were used to excavate tunnels. Stepped slabs were dug into the chalk, allowing many miners to dig at the same time. Care had to be taken to ...
The weight of overlying sediments caused the deposits to become consolidated into chalk. [9] British chalk deposits are considered stratigraphically to belong in the Chalk Group. Evidence of erosion along the cliff top. Due to the Alpine orogeny, a major mountain building event during the Cenozoic, the sea-floor deposits were raised above sea ...
The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. The density correspondingly ranges from 1.5 to 2.7 g/cm 3 . Although relatively soft, with a Mohs hardness of 2 to 4, dense limestone can have a crushing strength of up to 180 MPa . [ 13 ]
Chalk is applied to the tip of the cue stick, ideally before every shot, to increase the tip's friction coefficient so that when it impacts the cue ball on a non-center hit, no miscue (unintentional slippage between the cue tip and the struck ball) occurs. Chalk is an important element to make good shots in pool or snooker.
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.
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. Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.