mineral

Aragonite

Aragonite (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3.5-4 on Mohs scale; Color: Usually white, colorless, gray, yellow, green, or violet; Luster: Vitreous to resinous; Crystal structure: Orthorhombic, often forming prismatic, acicular (needle-like), fibrous, or stalactitic habits. Can also form pseudo-hexagonal twinned crystals.…

Hardness: 3
Color: Usually white, colorless, gray, yellow, green, or violet
Luster: Vitreous to resinous

Identified October 24, 2025More mineral →

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Physical properties

Formation & geological history

Aragonite forms in a variety of low-temperature environments, often biologically mediated. It is the metastable polymorph of calcium carbonate at surface pressures and temperatures, eventually transforming to calcite over geological time. It can form in marine and freshwater environments, hot springs (as tufa), caves (as stalactites and stalagmites), and in the shells of marine organisms. Geological age varies greatly depending on the specific formation.

Uses & applications

While less common than calcite, aragonite is used in soil conditioners, as an ornamental stone, and sometimes in jewelry (especially iridescent forms like 'pearl' aragonite). It is also scientifically important for paleoclimate studies.

Geological facts

Aragonite is a polymorph of calcite, meaning it has the same chemical composition (CaCO3) but a different crystal structure. This difference makes aragonite less stable at surface conditions and it gradually converts to calcite. Organisms like corals, mollusks, and some algae precipitate aragonite for their shells and skeletons.

Field identification & locations

Identify in the field by its crystal habit (often acicular or pseudo-hexagonal), its moderate hardness (scratches easily with a knife, but not with a fingernail), and its effervescence in dilute hydrochloric acid (like calcite). It can be distinguished from calcite which usually has rhombohedral cleavage. Commonly found in hot spring deposits (e.g., Carlsbad, New Mexico; various locations in Europe), caves, and certain marine sediments. For collectors, well-formed crystal clusters are prized.

Other mineral specimens

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Gneiss or Schist

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Metamorphic

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Calcite–fluorite mineral specimen with iron-oxide staining

Calcite (CaCO₃), likely fluorite (CaF₂), with possible quartz and iron/manganese oxides

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Mineral Sand (Heavy Mineral Sand Concentrate)

Placer deposit concentrate containing minerals such as ilmenite, rutile, zircon, and magnetite

mineral

Septarian Pebble

Septarian nodule / Concretion

sedimentary

Soil with Mineral Detritus and Quartz Fragments

Regolith / Silicate Mineral Aggregate

sedimentary