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Crystal structure of calcite. Calcium carbonate is a chemical compound with the chemical formula Ca CO 3.It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls.
Calcareous speleothems form via carbonate dissolution reactions whereby rainwater reacts with soil CO 2 to create weakly acidic water via the reaction: [3] H 2 O + CO 2 → H 2 CO 3. As the acidic water travels through the calcium carbonate bedrock from the surface to the cave ceiling, it dissolves the bedrock via the reaction: CaCO 3 + H 2 CO ...
Calcium carbonate is the active ingredient in agricultural lime, and is created when Ca ions in hard water react with carbonate ions creating limescale. It is commonly used medicinally as a calcium supplement or as an antacid, but excessive consumption can be hazardous.
The calcium carbonate layers in a shell are generally of two types: an outer, chalk-like prismatic layer and an inner pearly, lamellar or nacreous layer. The layers usually incorporate a substance called conchiolin , often in order to help bind the calcium carbonate crystals together.
Foraminifera typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure. [8] These shells are commonly made of calcium carbonate (CaCO 3) or agglutinated sediment particles. Over 50,000 species are recognized, both living (6,700–10,000) [9] [10] and fossil (40,000).
The calcareous sponges [2] [3] (class Calcarea) are members of the animal phylum Porifera, the cellular sponges.They are characterized by spicules made of calcium carbonate, in the form of high-magnesium calcite or aragonite.
The largest biosilica structure on Earth is the giant basal spicule from the deep-sea glass sponge Monorhaphis chuni. [19] The diagram on the right shows: (a) Young specimens of M. chuni anchored to the muddy substratum by one single giant basal spicule (gbs). The body (bo) surrounds the spicule as a continuous, round cylinder.
The calcium carbonate that the otolith is composed of is primarily derived from the water. As the otolith grows, new calcium carbonate crystals form. As with any crystal structure, lattice vacancies will exist during crystal formation allowing trace elements from the water to bind with the otolith.