Ammolite

Ammolite comes from the Bearpaw Formation, marine shales laid down 70–75 million years ago in the Western Interior Seaway. Although the formation also crops out in Saskatchewan and Montana, commercial ammolite has been reported only from southern Alberta, mainly along the St. Mary River southwest of Lethbridge. The gem layer is typically found in siderite (ironstone) concretions; deeper burial in that area is thought to have intensified the colors, while near-surface shell has altered to white calcite with no gem value. Korite International has been the dominant producer.

Ammolite shows vivid iridescence from interference of light in thin aragonite layers; much of it shows numerous flat panes of uniform color separated by fractures that were naturally refilled with carbonate or clay (fractured ammolite), while sheet ammolite shows little or no crushing. Check how a stone is built: a triplet has a colorless synthetic spinel or quartz cap over a very thin ammolite layer (about 0.1 mm in an average triplet) on a dark shale backing, a doublet has only a backing, and a solid is ammolite on its natural matrix or on both sides. Epoxy stabilization of solids and doublets appears only as very thin seams and small filled voids between layers, recognizable with difficulty above 30× magnification. Iridescent ammonites from Utah, England, Morocco or Madagascar are usually too thin, patchy or weak for gem use.

Ammolite is soft (Mohs 3.5–4), brittle and can cleave on impact. Uncapped stones are best used in earrings, brooches, pins and pendants, where abrasion and impact are less likely; capped triplets protect the thin colored layer.

According to geology.com, the Blackfoot people knew iridescent ammonite for hundreds of years, called it "Iniskim" (buffalo stone) and used it as a talisman. The Geological Survey of Canada recognized the ammonites in 1908; amateur lapidaries first showed cut pieces at a gem show in Nanton, Alberta, in 1962, and in 1967 Calgary jeweler Marcel Charbonneau introduced the name "Ammolite". Other trade names followed (Calcentine in 1975, Korite in 1981), and in 1981 the CIBJO Colored Stones Commission accepted Ammolite as a permitted name for aragonite. Japanese tourism to the Canadian Rockies made it widely known in Japan in the 1980s, and in 2004 it became Alberta's official gemstone.

The Japanese retailer Pascle says ammolite is believed to bring good fortune and strength to its owner and notes interest from feng shui practitioners, and it retells a legend in which Indigenous people of Alberta found the shining stone in the snow before the buffalo returned. These are retailer-attributed beliefs, not verified effects.