aragonite

{{Infobox mineral | name = Aragonite | boxwidth = | boxbgcolor = Orange | image = Aragonite crystal - Los Molinillos, Ceunca, Spain - 4x3.6x3.5cm 100g.jpg | imagesize = | alt = | caption = Aragonite from Los Molinillos, Cuenca, Spain, sample width about 4 cm | category = Carbonate minerals | formula = | IMAsymbol = Arg (not to be confused with arginine) | molweight = | strunz = | dana = | system = Orthorhombic | class = | symmetry = | unit cell = l a = 4.9598(5) Å, b = 7.9641(9) Å, and c = 5.7379(6) Å at 25 °C | color = Can come in a variety of colors, but commonly red or white | colour = | habit = Commonly dendritic or pseudo-hexagonal; can also be acicular, tabular, prismatic, coral-like | twinning = Cyclic on {110}, forms pseudohexagonal aggregates. If polysynthetic, forms fine striations parallel to [110]. | cleavage = Good on [110], Poor on {110}. | fracture = Subconchoidal | tenacity = Very brittle | mohs = 3.5–4 | luster = Vitreous, waxy, resinous | streak = White | diaphaneity = Transparent to opaque | gravity = 2.94 | density = | polish = | opticalprop = Biaxial (−) | refractive = nω = 1.550 nε = 1.650 | birefringence = δ = 0.155 | pleochroism = | 2V = Measured 18–19° | dispersion = Weak | extinction = Parallel | length fast/slow = | fluorescence = Faint white-blue to blue-violet | absorption = | melt = | fusibility = | diagnostic = | solubility = Soluble in acids, and saltwater (but takes longer) | impurities = Commonly strontium, zirconium, lead | alteration = | other = Thermodynamically unstable, Morphs slowly back into calcite | prop1 = | prop1text = | references = }}

Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.