Coral Gemstones – Properties, Origins, Treatments and Buying Guide

Coral is one of the oldest gemstone materials known to humanity, valued for its organic origin, rich colours and cultural significance. Unlike mineral gemstones formed deep within the earth, coral is created by living marine organisms and has been used in jewellery, amulets and carvings for thousands of years.

In this guide we examine coral from a professional gemmological and commercial perspective, covering its physical properties, structure, treatments, origins and how to identify fine-quality material.

Coral is an organic gemstone formed from the skeletal remains of marine polyps. Over time, these calcium carbonate structures harden and can be cut and polished for use in jewellery.

Unlike mineral gemstones, coral does not crystallise. Its value depends on colour, density, surface quality and origin. Historically, coral has been associated with protection, vitality and status.

Coral is composed primarily of:

Calcium carbonate (CaCO₃)

Minor organic compounds and trace elements contribute to colour variation and structure.

Because coral is organic, its composition differs significantly from crystalline gemstones.

Coral is classified as an organic gemstone rather than a mineral.

It does not belong to a crystal system. Instead, it forms in branching or massive structures created by marine organisms.

Coral is valued for its smooth polish, distinctive colour and organic texture rather than brilliance.

Lustre
Dull to vitreous when polished.

Transparency
Opaque.

Refractive index
Approximately 1.48 – 1.66 depending on density.

Specific gravity
2.60 – 2.70.

Coral occurs in a variety of colours:

Red
Pink
Salmon
White
Black

Red and deep pink coral are traditionally the most valuable colours.

Coral has a Mohs hardness of 3 to 4, making it relatively soft.

It is best suited for earrings, pendants and occasional-wear jewellery rather than daily rings.

Most coral on the market is treated to improve colour and durability.

Common treatments include dyeing, waxing and resin impregnation. These treatments should be disclosed at sale.

Avoid ultrasonic and steam cleaners.
Avoid acids, perfumes and cosmetics.
Clean gently with a soft cloth and mild soap if necessary.
Store coral separately from harder gemstones.

Major sources of coral include:

Mediterranean Sea (Italy, Spain)
Algeria
Japan
Taiwan
Thailand
Red Sea
Indonesia