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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The influence of organic matrices in the secretion of polymorphs of calcium carbonate by mollusks is well known. Recent work on the ultrastructure of coralline algae indicates that an organic matrix also must be involved in the secretion of high-Mg calcite by these plants. The matrices of coralline algae are on a much lower level of organization than the matrices of the mollusks.
Two genera of coralline algae have been studied using the scanning electron microscope. The genus Lithophyllum is characterized by a smooth lamellar ultrastructure which is parallel with the growth surface. The genus Goniolithon displays a rough lamellar ultrastructure in which the lamellae are parallel with the cell walls and consist of randomly oriented, blunt prisms of calcite.
It is known that organic molecules in solution are adsorbed onto mineral surfaces. Such adsorbed molecules could act as simple organic matrices and control the mineralogy of so-called "inorganic cements." Experiments have been conducted using completely inorganic chemical systems and systems of mixed organic and inorganic solutions. These experiments indicate that the presence of organic molecules in the system does exert a definite influence upon the mineralogy of the precipitated cements. Both calcite and aragonite cements have been produced in the laboratory under ambient temperatures and pressures.
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