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Calcareous rock
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Calcareous rock
A rock composed mainly of calcium carbonate (calcite).
Calcareous soil
A soil containing free calcium (and which is therefore usually fertile).
Calcite
The main element in limestone and also in many animal shells. It is extracted by living things directly from seawater and then made into shells.
Calcite (calcium carbonate) is colourless or white, but often occurs as grains rather than crystals mixed with other materials, such as clay. In this case the rock looks grey.
Calcite is soft (3 on Mohs’ scale of hardness) and commonly found in sedimentary rocks. It is also found in metamorphic rocks as marble. Calcite is readily dissolved by water. (See also: Gangue.)
Cap rock
A rock that overlies other rocks and protects them in some way. A cap rock can make the lip to a waterfall, the flat top surface of a plateau, or the impermeable rock that traps oil or water below it.
(See also: Aquiclude; Petroleum; Reservoir rock.)
Carbonate minerals
Minerals that contain carbon and oxygen (carbonates, for example, calcite, calcium carbonate).
 Chalk – Chalk is a soft, white rock that can make spectacular cliffs. These are near Dover.
Central vent volcano
(See: Stratovolcano.)
Chalk
A soft limestone rock made
of the skeletons of microscopic sea creatures. Chalks are soft
and permeable rocks. They form massive beds and produce striking landscape features such as the White Cliffs of Dover (See also: Calcite.)
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