Coral: The Complete Guide

Coral is one of the most ancient gem materials in human use, yet it occupies one of the most ethically complex positions in the modern jewellery market. Red and pink coral from Mediterranean and Pacific sources has been used in jewellery and decorative arts for at least 30,000 years. It carries deep cultural significance across Mediterranean, Tibetan, Native American, and Asian traditions. It also raises serious sustainability concerns that any conscientious jewellery professional must navigate carefully.

What Coral Is

Gem coral is the skeletal material of marine invertebrates belonging to the order Gorgonacea and related groups. The skeleton is composed of calcite (and in some species, conchiolin) secreted by coral polyps. Precious coral grows in deep, cold, dark marine environments — typically 50 to 2,000 metres below the surface — in the Mediterranean Sea, Pacific Ocean (Japan, Taiwan, Hawaii), and Atlantic Ocean.

The classic gem coral is Corallium rubrum (Mediterranean red coral) and Corallium japonicum (Japanese/Taiwanese red and pink coral). Other colour varieties include angel skin (pale pink to near-white), Momo (peach to salmon pink), and black coral (from a different organic composition). Coral has a Mohs hardness of 3-4, making it very soft and suitable primarily for pendants, earrings, and beads rather than rings.

Varieties and Quality

Ox Blood (Deep Red) Coral

The most valuable coral is the deep, rich red called “ox blood” — an even, saturated red without pale centres, surface pitting, or white marks. Fine ox blood Mediterranean coral is the most prized and commands the highest prices. Japanese moro coral approaches this quality level. The colour should be even throughout without the lighter centres often seen in lower-quality material.

Angel Skin Coral

Angel skin coral is a pale pink to near-white variety with a delicate, porcelain-like appearance. It is highly prized in Asian markets, particularly Japan and China, where its pale, refined colour is associated with feminine beauty and purity. Fine angel skin coral with even, unblemished surface and good lustre is rare and valuable.

Conservation and Ethical Sourcing

Precious coral populations have been severely depleted by overharvesting, climate change, and ocean acidification. CITES (the Convention on International Trade in Endangered Species) regulations apply to some coral species. The US Lacey Act makes it illegal to import coral harvested in violation of other countries’ laws. Many nations have harvest quotas or outright bans on coral collection.

The ethical sourcing of coral requires documentation of legal harvest, country of origin, and compliance with applicable regulations. Antique and vintage coral jewellery (pre-1973, before CITES came into force) is generally tradeable without the restrictions applying to newly harvested material. For new coral purchases, provenance documentation is essential.

Treatments and Imitations

Coral is widely treated with dyes (to deepen or even colour), surface coatings, and impregnation with resins or wax to improve surface quality. Reconstructed coral (coral powder bound with resin) is also sold commercially. Imitations include dyed bone, dyed shell, plastic, glass, and synthetic materials. The hot needle test (resin melts, natural coral does not burn in the same way) and magnification examination are preliminary tests; definitive identification requires FTIR or Raman spectroscopy.