- Form in shallow seas, when grains of sand or shell fragments are rolled around by currents and accumulate a layer of calcium carbonate around the centre.
- Due to the above, they are formed by Chemical Processes.
- Only formed in strong currents, and only forms in hot climates in which, calcium carbonate is precipitated.
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Fossiliferous Bioclastic or Shelly Limestone
- Potentially 75% of the rock may be composed of invertebrate skeletons from crinoids, brachiopods or mixtures of fossils. (Gonna have to look those things up).
- Rest of rock is calcite mud and ordinary detrial mud.
- The rock has a grey colour and has easilly visable fossils.
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- Rich in corals and algea which build up the framework.
- Form in warm, shallow tropical waters.
- Are unbedded as they grow upwards.
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- Purest of the limestones, containing only a tiny amount of mud or sand.
- White, hard, often massive and well jointed.
- Mostly formed by the remains of a microscopic algae called a coccolith.
- Formed in medium depth water (200m), note that landmasses contribute very little to the formation of chalk.
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- Fine, hard crystaline limestone, that shows no features.
- Formed by purely calcite mud which has undergone diagenisis.
- No fossils visable.
- Formed in low energy, shallow water environments e.g. lagoons.
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