Bamboo Coral (Keratoisis)
Bamboo coral (Umitake) is named for its bamboo-like appearance, caused by the alternating growth of white calcareous (carbonate) segments and black-brown organic nodes. In the international market, it is known as Bamboo Coral. As it was originally rarely found in colored varieties, it was not often used for decorative purposes; however, in recent years, caution is required when handling it as it is sometimes bleached and sold as "white coral" or dyed to resemble "red coral." Classified as a hexacoral, its skeletal axis is organic rather than calcite, making it relatively resistant to acid. However, it is prone to cracking and warping when dehydrated.
The unique look created by its bamboo-like layered structure. It is a material often subject to "imitation processing" in the trade.
Basic Information
| English Name | Keratoisis (often traded as Bamboo Coral) |
|---|---|
| Japanese Name | Umitake (Bamboo Coral) |
| Chemical Composition | CaCO3 + MgCO3, and other organic matter |
| Structure | Aggregate of fine crystals |
| Hardness | 3.5–4 |
| Specific Gravity | 2.6 |
| Classification | Organic gemstone (coral) |
Features and Variations
- Visual Features: White calcareous segments and black-brown organic segments grow in an alternating pattern, creating a bamboo-like appearance.
- History of Use and Trade Precautions: While originally little used for decoration due to a lack of naturally colored varieties, it is currently sometimes bleached to pass as "white coral" or dyed to resemble "red coral."
- Properties: Classified as a hexacoral, its organic skeletal axis makes it resistant to acid, but it is susceptible to cracking and deformation upon dehydration.
Trade Names and Commercial Names
- Mountain Coral (Yama Sango): Sometimes used as a trade name for specimens dyed red.
- Umitake/White Coral: Specimens bleached to a pure white color may be sold as "white coral."
Treatments
- Dyeing: Dyed in various colors to imitate red, Angel Skin (Boke), or pink corals.
- Bleaching: Performed to achieve a pure white look, often for the purpose of imitating white coral.
Similar Stones
- White Coral: When compared, the skeletal tissue structure differs, showing fine concentric patterns. Additionally, bamboo coral is generally considered to have higher translucency.
Caution: Bamboo coral is frequently subject to "imitation processing" via bleaching and dyeing. If you see labels like "white coral" or "mountain coral," verify that the material's actual composition matches the description of any treatments applied. Also, as it is prone to cracking and warping due to dehydration, be mindful of the storage environment (avoiding excessive dryness and heat).