aragonite

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aragonite Mineral, CaCO3; sp. gr. 2.9; hardness 3.5–4.0; orthorhombic; colourless, white, grey, or yellowish; white streak; vitreous lustre; crystals normally prismatic, often acicular, sometimes tabular and pseudo-hexagonal; also occurs fibrous and stalactitic; cleavage imperfect cleavage; occurs in hot springs and in association with gypsum, also in veins and cavities, and in the oxidized zone of ore deposits with other secondary minerals. Aragonite is a polymorph of calcite, from which it is distinguished by its lack of cleavage and its higher specific gravity. Calcite is the more stable form of CaCO3, and many fossil shells that were made originally of aragonite have either converted to calcite or undergone replacement by some other mineral. Present-day mollusc shells are formed of aragonite crystals. The name is derived from the Aragon province of Spain. See also CARBONATES.

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aragonite A colourless, white, grey, or yellowish mineral (CaCO3) that occurs in hot springs and in association with gypsum, also in veins and cavities, and in the oxidized zone of ore deposits with other secondary minerals. Aragonite is a polymorph of calcite, from which it is distinguished by its lack of cleavage and its higher specific gravity (2.9). Calcite is the more stable form of CaCO3 and many fossil shells that were made originally of aragonite have either been converted to calcite or undergone replacement by some other mineral. Present-day mollusc shells are formed of aragonite crystals. The name is derived from the Aragon province of Spain. Aragonite usually occurs as prismatic or acicular crystals but is sometimes fibrous and stalactitic.

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aragonite A form of calcium carbonate (CaCO3) from which the shells of many invertebrates (e.g. Mollusca) are formed. It is less stable than calcite and in many fossil shells aragonite has been converted to calcite or been replaced by other minerals. The name is taken from the Aragon province of Spain.