The BCCF - for information about calcium carbonate

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Calcium Carbonate

The World's Most Versatile Mineral

Calcium Carbonate Glossary


Chalk is a poorly compacted sedimentary rock predominately composed of compacted coccoliths (a lime-secreting algae).


Formed as limestone (see below) but the sedimentation process occurs in the presence of magnesium resulting in a dolomitisation process.


Limestone is also a sedimentary rock, but it is more compacted than chalk. It is formed from the remains of microscopic animals or foraminifera.


Marble is a coarse-crystalline, metamorphic rock, which is formed when chalk or limestone are recrystallised under conditions of high temperature and pressure.

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Calcium Carbonate – geology

A story spanning over 200 million years of the UK's history

UK calcium carbonate geology is based on 3 principal resources: Carboniferous limestone, Cretaceous chalk and Dolomite (a mixed carbonate of calcium and magnesium).

With the exception of dolomite all have the same chemical formula but due to distinct differences in there formation, have different properties.

Sedimentation and rock formation

Original carbonate deposition

calcium carbonate deposition

Flat land surface. Shallow, warm sea. Minimal sediment washed in from land. Deposition of calcium carbonate in skeletons of marine organisms

Sedimentation is the rock forming process from which all limestones, including chalk and, ultimately, marble originate.

Sedimentary rocks generally form in two stages: initially loose materials are deposited in layers, and then they are consolidated to rock by pressure or cementation. The physical, chemical or biological alteration of sediments into sedimentary rock is called diagenesis.

Rocks of biological origins

Most significant limestone deposits are derived from organogenic sedimentation meaning the original material forming the basis of the rocks is of biological origin. This mainly concerns the inorganic remains of invertebrates which deposit on the seabed and become consolidated in the course of time. The size of the component elements range from whole and broken shells of molluscs to coccoliths (single-called marine algae) measuring a few thousandths of millimetre.

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