Aragonite

Aragonite is a calcium carbonate mineral with an orthorhombic crystal structure. It is one of the two common naturally occurring crystalline forms of calcium carbonate, alongside calcite.

Calcium carbonate: Calcium carbonate is a chemical compound, CaCO₃, found in minerals, rocks, shells, and skeletons. Aragonite is one crystalline form of this compound.
Aragonite saturation state: Aragonite saturation state measures whether seawater favors aragonite precipitation or dissolution. It indicates how readily seawater can sustain or form aragonite.
Mollusk shell: A mollusk shell is a hard external structure made by a mollusk, commonly from calcium carbonate and organic material. Many mollusk shells contain aragonite layers.
Calcite: Calcite is a calcium carbonate mineral with a trigonal crystal structure and is the most stable common form of CaCO₃ at Earth’s surface. Calcite shares aragonite’s composition but has a different crystal structure and greater surface stability.
Ocean acidification: Ocean acidification is the long-term decline in ocean pH caused mainly by absorption of atmospheric carbon dioxide. Lower carbonate availability makes aragonite harder for marine organisms to form.
Orthorhombic crystal system: The orthorhombic crystal system has three mutually perpendicular axes of unequal length. Aragonite’s crystal lattice belongs to this system.
Biomineralization: Biomineralization is the process by which organisms produce minerals within or around their tissues. Marine organisms can guide calcium carbonate formation into aragonite.
Pearl: A pearl is a layered biomineral formed within a mollusk, usually from aragonite and organic matrix. Its nacre commonly consists of aragonite platelets bound by organic material.
Vaterite: Vaterite is a rare, metastable crystalline form of calcium carbonate. It is a less common CaCO₃ polymorph that can transform into calcite or aragonite.
Aragonite compensation depth: The aragonite compensation depth is the ocean depth below which aragonite dissolves faster than it accumulates. It marks the depth limit for long-term preservation of aragonite sediments.

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