biomineralization The incorporation of inorganic compounds, such as salts, into biological structures, often to lend them hardness or rigidity. Biomineralization first occurred in, and defines, the Cambrian period about 590 million years ago, in Brachiopoda, Trilobita, Ostracoda, and Graptolithina. In vertebrates, hydroxyapatite usually occurs, in invertebrates inorganic minerals are more varied: calcite and aragonite (a harder, less stable form of calcite) are common, permeating chitin (see SKELETAL MATERIAL) to form the hard exoskeletons of Arthropoda and also forming the calcareous material of shells; in Radiolaria and some Porifera, the skeleton is made of opaline silica; Radiolarians occasionally have a strontium sulphate instead of siliceous skeleton.

biomineralization The incorporation of inorganic compounds, such as salts, into biological structures, often to lend them hardness or rigidity. Biomineralization first occurred in, and defines, the Cambrian period about 542 million years ago, in brachiopods, trilobites, ostracods, and graptolites (Graptolithina). In vertebrates, hydroxyapatite usually occurs, in invertebrates inorganic minerals are more varied: calcite and aragonite (a harder, less stable form of calcite) are common, permeating chitin to form the hard exoskeletons of Arthropoda and also forming the calcareous material of shells; in Radiolaria and some Porifera, the skeleton is made of opaline silica; radiolarians occasionally have a strontium sulphate instead of siliceous skeleton.