Black coral
Organic gem
About it
A horny protein skeleton, not stone, so it is light and warm, with fine growth rings in cross-section. All black corals are listed on CITES Appendix II; Hawaii's state gem.
- Type
- Organic gem
- Group
- Coral skeleton (protein)
- Hardness (Mohs)
- 2.5–4
- Specific gravity
- 1.3–1.45
- Lustre
- waxy, resinous
- Colours
- black, dark brown
- Transparency
- opaque
- Cleavage and fracture
- none; uneven fracture
Typical values: real specimens vary. For more, see mindat.org.