Aragonite

AragoniteFromCrystalMaker

P-T Diagram for CaCO3

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BaculitesSuturesAragonite

Aragonite is a carbonate mineral, one of the two most common, naturally occurring, crystal forms of calcium carbonate, CaCO3 (the other form being the mineral calcite). It is formed by biological and physical processes, including precipitation from marine and freshwater environments. Aragonite's crystal lattice differs from that of calcite, resulting in a different crystal shape, an orthorhombic system with acicular crystals. Repeated twinning results in pseudo-hexagonal forms. Aragonite transforms to calcite at 380-470°C, but is relatively stable at room temperature.

Formation and Locations

Aragonite forms naturally in almost all mollusk shells, and as the calcareous endoskeleton of warm- and cold-water corals (Scleractinia). Because the majority of marine organisms prefer aragonite for their shell and skeleton formation, the mineral is of significant importance in the carbon cycle.

Aragonite is also found in serpentine rocks as a product of metamorphism and in hydrothermal vents. Aragonite precipitates by physical processes such as evaporation in marine and freshwater environments. Notable locations for aragonite include Mexico, Namibia, and the Bahamas, where it forms in caves as stalactites and stalagmites.

Uses

Aragonite has several applications. It is used primarily in the aquarium industry as a substitute for live rock, for maintaining alkalinity and for its buffering capabilities. In agriculture, powdered aragonite is a valuable fertilizer and soil conditioner. It is also used in the manufacture of glass and ceramics and has been investigated for carbon sequestration.

Environmental Significance

Aragonite plays a crucial role in the biogeochemical cycles of carbon and calcium. Its formation and dissolution in the ocean are key processes in the global carbon cycle, influencing carbon dioxide levels in the atmosphere and, consequently, global climate change. The ongoing acidification of the oceans poses a threat to aragonite, as it becomes more soluble in acidic conditions, affecting marine organisms that rely on it for their skeletal structures.

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See Also

• Calcite
• Carbon cycle
• Marine biology
• Sedimentary rock
• Mineralogy