Ammolite

Properties and Origin

• Variable chemical composition, including aragonite, calcite, silica, pyrite, and other minerals
• Orthorhombic crystal structure
• Hardness of 3.5-4.5 on the Mohs scale
• Specific gravity of 2.60-2.85g/cm³
• Fluoresces a mustard yellow under ultraviolet light
• Ammolite comes from the fossil shells of ammonites, specifically Placenticeras meeki, Placenticeras intercalare, and Baculites compressus
• Ammonites thrived in a prehistoric subtropical sea that bordered the Rocky Mountains, known as the Cretaceous or Western Interior Seaway
• Ammonites sank to the bottom of the sea and were buried by layers of mud, eventually becoming shale
• Gem-quality ammonites are found within siderite concretions
• Sediments preserved the aragonite of the shells, preventing it from converting to calcite

Occurrence and Extraction

• Significant deposits of gem-quality ammolite are found in the Bearpaw Formation, extending from Alberta to Saskatchewan in Canada and south to Montana in the USA
• Small deposits have been found as far south as Central Utah
• Best grade of gem-quality ammolite is found along high energy river systems on the eastern slopes of the Rockies in southern Alberta
• Most commercial mining operations are conducted along the banks of the St. Mary River, between the town of Magrath and the city of Lethbridge
• Roughly half of all ammolite deposits are contained within the Kainah reserve
• Commercial extraction is mechanized, involving shallow open pits dug with an excavator
• Excavated material is screened for potential gem contents
• Pits are further examined by hand
• Approximately 50% of mined ammolite is suitable for jewelry
• Korite, the largest miner of ammolite, produces over 90% of the world's supply

Other Names and Imitations

• Ammolite is also known as aapoak (Kainah for small, crawling stone), gem ammonite, calcentine, and korite
• The trade name 'korite' was given to the gemstone by the Alberta-based mining company Korite
• Marcel Charbonneau and Mike Berisoff were the first to create commercial doublets of the gem in 1967
• They formed Ammolite Minerals Ltd.
• In 1981, ammolite was given official gemstone status by the World Jewellery Confederation (CIBJO)
• Labradorite and broad-flash black opal have a passing resemblance to ammolite but are not convincing substitutes
• Slocum stone, a glass-based imitation of opal, is even less convincing with tinsel-like patches of play of color
• Ammolite can be grouped with shell-based marbles like lumachella, but the iridescence of lumachella is not as brilliant
• Ammolite is often used as an imitation of black opal, which is actually of greater value

Gemstone Quality and Value Factors

• The quality of gem ammolite is graded using a letter system (AA, A+, A, A-) but is not standardized
• Primary colors in ammolite include red, green, blue, and purple, with red and green being more common
• The rarest and most valuable ammolite grades have three or more primary colors or 1-2 bright and even colors
• Chromatic shift refers to how the colors vary with the angle of viewing, while rotational range is how far the colors can be turned
• The brightness of colors and iridescence depend on the preservation of the nacreous shell and the fine layers of aragonite
• The number of primary colors and the presence of rare hues like crimson or violet affect the value of ammolite
• Higher-grade ammolite shows a prismatic variation in chromatic shift, while lower grades have little variation
• The brightness of colors and iridescence depend on the preservation of the nacreous shell and the quality of polish
• Thicker ammolite layers, without visible matrix or foreign minerals, are more valuable
• Calibrated stones and minimal treatment increase the value of ammolite gems

Use in Jewelry and Market

• Ammolite is best suited for use in pendants, earrings, and brooches due to its fragility
• It gained interest in Western society in the 1970s and entered the market in 1969
• The Blackfeet tribe believes ammolite, known as 'iniskim,' possesses amuletic powers
• Practitioners of feng shui promote ammolite as a stone that enhances well-being and detoxifies the body
• Ammolite is usually fashioned into freeform cabochons and mounted in gold, often with diamond accents
• Japan is the largest market for ammolite
• Ammolite is used as an imitation of black opal, which is becoming scarce
• Canada is another market for ammolite, used by artisans and fine jewelry producers
• Ammolite is crafted in the Southwest United States by Native American craftspeople
• It is popular among tourists visiting Banff National Park and Jasper National Park

Ammolite Data Sources