Aragonite
Aragonite is a mineral composed of calcium carbonate, named after the Aragon region in Spain where it was first discovered. It is a polymorph of calcite, meaning it shares the same chemical composition but has a different crystal structure. It is often formed in low-temperature environments as the primary component of shells and pearls, and has long been appreciated for its beauty in the form of "bunseki" (or ornamental aragonite) and stalactites.
Aragonite featuring beautiful patterned formations
Basic Information
| English Name | Aragonite |
|---|---|
| Japanese Name | Ara-ishi (霰石) |
| Chemical Formula | CaCO3 |
| Crystal System | Orthorhombic (often pseudo-hexagonal) |
| Hardness | 3.5–4 |
| Specific Gravity | Approx. 2.94 |
| Transparency | Transparent to translucent |
Characteristics & Varieties
- Ornamental Aragonite (Bunseki): Formed by precipitation within the pores of basalt from the Penghu Islands, Taiwan; it often resembles agate.
- Cave Pearls: Spherical formations created in limestone caves using grains of sand as nuclei.
- Aragonite Agate: Banded varieties that exhibit stripes.
- Pseudo-hexagonal: Often exhibits pseudo-hexagonal crystals formed by the twinning of three individual crystals.
Origin, Aliases, Treatments, & Simulants
Primary Origins: Spain, Taiwan, Shirahama Onsen (Wakayama, Japan), and Yufuin Onsen (Oita, Japan).
Alias: Bean stone (for those found in hot spring areas).
Treatment: Dyeing (Gem-quality aragonite is often dyed green and sold as an imitation of jade).
Simulants: Calcite (Although they share the same composition, their crystal systems differ; they are difficult to distinguish without gemological testing).
Care Instructions: With a low hardness of 3.5–4, it can be scratched by a needle. It is also sensitive to heat and acid, and will effervesce and dissolve in diluted hydrochloric acid, so please handle it with great care.