Ammolite: The Complete Guide
Ammolite is one of the rarest organic gem materials in the world and one of the most visually spectacular. It is the iridescent shell material of ancient ammonite fossils, approximately 65 to 71 million years old, found commercially only in a small area along the St. Mary River in southern Alberta, Canada. Its play of colour — brilliant, shifting spectral hues of red, green, gold, blue, and purple — is produced by light interference in the thin aragonite layers of the fossil shell and rivals opal and labradorite in visual drama. Ammolite has been recognised as a gem material by CIBJO only since 1981 and is still being established in mainstream fine jewellery.
What Ammolite Is
Ammolite is the trade name for the iridescent fossil shell material of ammonites — extinct cephalopod molluscs related to modern nautilus and octopus — that lived from approximately 200 million to 65 million years ago. The ammolite gem material comes specifically from Placenticeras meeki and Placenticeras intercalare species preserved in the Bearpaw marine shale formation of southern Alberta. The iridescent colours are produced by light interference in thin layers of aragonite (a form of calcium carbonate) that make up the original shell nacre, preserved through the fossilisation process.
The ammolite layer is extremely thin — typically only 0.5 to 0.8 mm — and must be backed with the parent shale matrix or other material for stability. Most commercial ammolite is therefore a natural composite: the iridescent ammolite layer bonded to a matrix backing. Higher-quality ammolite may have a quartz or spinel cabochon cap added over the iridescent layer (creating a triplet similar in construction to opal triplets) for protection.
The Source: A Single River Valley
The commercial ammolite deposits are found primarily in a narrow strip along the St. Mary River near Lethbridge in southern Alberta, with the Korite International mining operation being the primary commercial producer. This geographic concentration — a single river valley in Canada — makes ammolite as geographically unique as tanzanite. The Blackfoot Nation of Canada has deep cultural connections to ammonite fossils, calling them “buffalo stones” (iniskim) and considering them sacred objects with protective properties. This cultural dimension adds depth to the ammolite narrative for interested clients.
Quality and Colour
Ammolite quality is assessed on the brightness and range of play of colour, surface coverage (percentage of the piece showing iridescence), pattern, and the presence of cracks (which reduce value). The most prized ammolite shows full-spectrum colour across the entire surface — vivid reds, greens, golds, and blues shifting as the piece moves. Red-dominant material is generally considered most valuable; blue is the rarest colour. Ammolite without cracks across the iridescent layer commands premium prices.
Commercial grades range from AA (finest, vivid full-spectrum colour without cracks) through A, B, and C grades of decreasing colour saturation and increasing crack presence. Standard commercial ammolite is graded and priced accordingly. Fine AA material in larger sizes is rare and commands prices that reflect genuine rarity.
