Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America.

It is commonly unearthed by natural erosion or through the process of various mining practices, within the perimeter of an ancient sea bed called the Western Interior Seaway.

The shell itself may contain a number of trace elements, including: Aluminium, barium, chromium, copper, iron, magnesium, manganese, strontium, titanium, and vanadium.

So-called "frost shattering" is common; exposed to the elements and compressed by sediments, the thin ammolite tends to crack and flake; prolonged exposure to sunlight can also lead to bleaching.

While these shells may be as large as 90 cm (35.5 inches) in diameter, the iridescent ammonites (as opposed to the pyritized variety) are typically much smaller.

The ammonites that form ammolite inhabited a prehistoric, inland subtropical sea that bordered the Rocky Mountains—this area is known today as the Cretaceous or Western Interior Seaway.

[7] Significant deposits of gem-quality ammolite have only been found in the Bearpaw Formation that extends from Alberta to Saskatchewan in Canada and south to Montana in the USA.

[6] The best grade of gem quality ammolite is along high energy river systems on the eastern slopes of the Rockies in southern Alberta.

Most commercial mining operations have been conducted along the banks of the St. Mary River, in an area south of and between the town of Magrath and the city of Lethbridge.

The pits are further examined by hand, and commercial production is supplemented by individuals who sell their surface-picked findings to Korite and several other producers.

Prospectors who wish to mine ammolite deposits on Crown land must apply to the Alberta Department of Energy for a lease.

The rarest and most valuable are thick enough to stand alone, with only a thin portion of its original matrix (not exceeding 1.5 mm); but the vast majority require some sort of supportive backing.

Ammolite is often damaged due to environmental exposure, even though it is fully mineralized and contains no water — therefore it is not subject to dehydration and subsequent crazing seen in opals.

In composites where the ammolite layer is exceptionally thin, a third component is used: This constitutes a triplet, with a durable and transparent convex topping piece.

The detection of these treated and composite stones is relatively simple via inspection with a loupe; however, certain jewelry setting styles—such as those with closed backs—can complicate things.

If the dome is made of glass, bubbles, swirl marks, and scratches may be present; the harder synthetic materials are optically flawless.

Although the vast majority of commercial-grade ammolite has been treated in some way, a small fraction of production requires no treatment other than cutting and polishing.

The visible structure is also considerably different; in the imitations, the body of the stone is transparent to translucent from certain angles, whereas ammolite is entirely opaque.

Under magnification most abalone doublets will show dye concentrated along certain areas and air bubbles trapped at the shell-quartz interface.

Compared to most other gems, ammolite has a rather scant history of use; it did not begin to garner interest in Western society until the 1970s after entering the market (to a limited degree) in 1969.

In the late 1990s, practitioners of feng shui began to promote ammolite as an "influential" stone with what they believe is the power to enhance well-being and detoxify the body by improving its flow of energy or "chi".

Japan is the largest market for ammolite; this may be due to its use as an imitation of increasingly scarce black opal, or its aforementioned use in feng shui.