Organic gems are ornamental materials produced by plants or animals instead of by purely geological processes. The group includes amber, pearl, coral, jet, ivory, shell and mother-of-pearl, plus fossil materials such as ammolite and petrified wood. Most are soft, light and sensitive to heat and chemicals, so they need more care than mineral gems. A few, such as elephant ivory and some corals, are restricted by wildlife law.
What counts as an organic gem
Gemologists use the label for anything whose substance came from a living organism, whatever its chemistry. Amber is hardened tree resin, a mix of organic compounds with no crystal structure. Jet is a compact form of fossil wood. Pearls, coral and shell are calcium carbonate laid down by animals, bound with protein. Ivory is dentine, the same tissue that makes up the bulk of a tooth.
Fossil materials sit at the edge of the group. In petrified wood, silica has replaced the original plant tissue, so the stone is mostly quartz in the shape of a tree. Ammolite keeps the original shell nacre of an ammonite. Many references list both because their origin is biological.
The main organic gems
| Material | Source | Mohs hardness |
|---|---|---|
| Amber | Fossil tree resin | 2-2.5 |
| Jet | Fossil wood | 2.5-4 |
| Pearl | Mollusks | 2.5-4.5 |
| Coral | Colonial marine animals | About 3-4 |
| Mother-of-pearl | Mollusk shell lining | About 3.5 |
| Ivory | Mammal tusks and teeth | About 2.5 |
| Petrified wood | Wood replaced by silica | 6.5-7 |
Each material has its own page. Read about natural pearls and conch pearls, mother-of-pearl and abalone, precious red coral, ivory and its legal limits, and fossils used in jewelry such as ammolite and agatized dinosaur bone. The history of amber and how amber is mined have separate pages too.
Why organic gems are soft and how to care for them
Apart from petrified wood, organic gems rank well below quartz on the Mohs hardness scale. Everyday dust contains quartz grains at hardness 7, so wiping or rubbing these materials can leave fine scratches over time. Pearl, coral and shell react with acids, including those in sweat, perfume and some cleaners. Amber softens with heat and is damaged by solvents such as acetone.
Simple habits protect them:
- Put organic jewelry on after perfume, hairspray and lotion.
- Wipe pieces with a soft damp cloth after wear.
- Keep them away from ultrasonic and steam cleaners.
- Store each piece in its own pouch, away from harder gems.
The guide to cleaning jewelry safely covers each type, and the page on gemstone durability compares organic gems with mineral stones.
Legal limits on ivory, coral and shell
Some organic materials come from protected species. International trade in wildlife products is governed by CITES, the Convention on International Trade in Endangered Species. African elephants were placed on its Appendix I in 1989, which ended most legal international trade in their ivory. Black coral and the stony reef-building corals are listed on Appendix II, so cross-border trade needs permits. Hawksbill turtle shell, once sold as tortoiseshell, is on Appendix I.
National and state laws often go further than CITES and change over time. Anyone buying, selling or traveling with ivory, coral or tortoiseshell should check the current rules in each country involved.
Organic gems in history
People wore organic materials long before they cut hard stones. Shell beads from Blombos Cave in South Africa are among the oldest known ornaments, and prehistoric jewelry also used bone, teeth and ivory. Baltic amber reached the Mediterranean in the Bronze Age, and Whitby jet became the standard material for Victorian mourning jewelry.
Frequently asked questions
Is pearl a mineral?
No. Pearl is made of aragonite, a mineral form of calcium carbonate, but a living mollusk produces it and binds it with organic protein, so gemologists class pearl as an organic gem.
Which organic gem is the hardest?
Petrified wood, at about 6.5 to 7 on the Mohs scale, because silica has replaced the original wood. Among the materials that keep their original substance, pearl and coral are slightly harder than amber, jet and ivory.
Is it legal to own ivory or coral jewelry?
Owning old pieces is often legal, but selling, buying or moving them across borders may be restricted. Rules vary by country and state, so check current local law before any sale or trip.