Pearl
Pearls are organic gemstones formed by layers of nacre secreted by mollusks within their bodies. In Japan, saltwater pearls are primarily produced in Mie and Wakayama Prefectures, while freshwater pearls are mainly sourced from Ibaraki and Shiga Prefectures. In 1893, Kokichi Mikimoto successfully cultivated pearls using Akoya oysters, marking a major turning point in the history of jewelry.
Pearls are prized for their elegant luster created by overlapping layers of nacre.
Basic Information
| English Name | Pearl |
|---|---|
| Japanese Name | Shinju (Pearl) |
| Chemical Composition | CaCO3 + organic substances (mainly conchiolin) |
| Hardness | 2.5–4.5 |
| Specific Gravity | Approx. 2.69 |
| Transparency | Opaque (a gemstone appreciated for surface luster) |
Characteristics & Varieties
- Cultivation Host Shells: Modern cultured pearls use various shells such as Akoya, South Sea (Silver-lipped and Gold-lipped), Tahitian (Black-lipped), Mabe, and Abalone.
- Freshwater Pearls: Freshwater pearls are produced using mussels such as the Ikecho, Japanese pond, and pearl mussels.
- Nature of Luster: The layered structure of nacre reflects and interferes with light, creating a soft glow (orient) and, in some cases, an iridescent shimmer.
Varieties
- Blister Pearl: A pearl that has grown attached to the inner surface of a shell.
- Wing Pearl: A natural pearl that forms near the hinge of certain freshwater bivalves.
Origin, Aliases, Treatments & Similar Stones
Main Production Areas (Japan): (Saltwater) Mie, Wakayama / (Freshwater) Ibaraki, Shiga
Treatments:
- Bleaching: Bleaching using chemical agents. Freshwater pearls can also be whitened via "light bleaching."
- Dyeing: Bleached pearls are tinted with dyes. Some methods involve using metal compound solutions.
- Irradiation: Exposure to gamma rays to produce shades of gray.
Related Information:
- Cave Pearl: Spherical cave deposits formed by spring water in limestone caverns.
- Pearl Spar: A white dolomite that exhibits a pearl-like luster when polished.
- Orient Effect: An iridescent luster visible depending on the thickness of the nacre (especially in Akoya pearls).
Important Notes: Pearls are low in hardness and sensitive to acid, dryness, and friction. Chemicals like perfume, hairspray, and detergents can cause deterioration, so put on jewelry last when dressing, and be sure to wipe off sweat and oils with a soft cloth after use. Also, since pearls may undergo bleaching, dyeing, or irradiation, always verify treatment information when purchasing.