Pearls are organic and are formed by living organisms. They are generally formed within the soft tissue layer of mollusks such as oysters and mussels. Pearls are composed of calcium carbonate (in the form of Aragonite) and organic conchiolin that build up as concentric layers as they are secreted by their host.
| Color | White, Pink, Silver, Cream, Brown, Green, Blue, Black, and Yellow |
| Mohs scale hardness | 2.5 – 4.5 |
| Specific gravity | 2.60 – 2.85 |