Quick Facts
Formation & Origin
Aragonite has the same chemical formula as calcite (CaCO₃) but a different crystal structure - they're polymorphs. Aragonite forms under higher pressure or lower temperature conditions than calcite, and in the presence of certain ions (especially magnesium and strontium) that inhibit calcite growth.
The most iconic aragonite form is the 'star cluster' or 'sputnik' variety from Morocco - radiating clusters of prismatic crystals that look like geometric sea urchins. These form in clay sediments where aragonite crystallizes from groundwater solutions. The clusters grow outward from a central point, creating the distinctive starburst shape.
Aragonite is metastable at Earth's surface conditions - over geological time, it slowly converts to the more stable calcite form. This means all aragonite specimens are relatively young in geological terms. Aragonite is also biologically important: it's the primary mineral in pearls, mother of pearl, and many marine shells.
Identification Guide
Aragonite is identified by its orthorhombic crystal habit (often as pseudo-hexagonal twins or radiating clusters), hardness of 3.5-4, and effervescence in dilute acid (confirming carbonate composition). The Moroccan star clusters are immediately recognizable.
Distinguish from calcite (different crystal system, rhombohedral cleavage), gypsum (softer, no acid reaction), and siderite (iron carbonate, higher SG). Aragonite's characteristic cyclic twinning produces pseudo-hexagonal forms that look hexagonal but have different cleavage.
Spotting Fakes
Aragonite star clusters from Morocco are abundant and inexpensive, making faking unnecessary. Some specimens are coated with iron oxide or other minerals to enhance color - this is natural in some cases but artificially applied in others. Blue aragonite from Namibia is genuine but sometimes enhanced. The main market confusion is between aragonite and calcite, which look different but share the same chemistry.
Cultural & Metaphysical Traditions
Presented as cultural traditions, not scientific evidence
Aragonite's association with Earth healing and grounding is its primary modern metaphysical connection. The star cluster form's resemblance to a root system or network reinforces this grounding association. Practitioners use it for environmental conservation meditation and connecting with Earth's energy. The biological connection to pearls and shells adds associations with patience, nurturing, and the ocean.
Where It's Found
Major source of star cluster and sputnik forms
Type locality, classic twin crystals
Blue aragonite specimens
Fine crystalline specimens, sulfur association
Price Guide
Good to Know
Scratch test: At hardness 3.5, Aragonite can be scratched with a copper coin. Handle gently and keep away from harder stones in your collection.
Sources: Found in 4 notable locations worldwide, from Morocco to Italy.
Heft test: Aragonite has average mineral density (2.93). It feels about as heavy as you'd expect from a stone its size.
Related Minerals
Same chemistry, different crystal structure (polymorph)
Made of aragonite layers deposited by mollusks
Third CaCO₃ polymorph, very rare
Related carbonate with strontium