Ammolite
Ammolite is a rare, opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains in North America. This unique gem is highly valued for its captivating iridescence and vibrant play of colors, which often includes shades of green, red, blue, and violet.
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Ammolite is formed from the fossilized shells of ammonites, ancient marine mollusks that thrived millions of years ago. These shells are primarily composed of aragonite, the same mineral found in nacre (mother of pearl). The microstructure of ammolite is inherited directly from the original ammonite shells, giving it a unique and striking appearance.
Ammolite is one of the few biogenic gemstones, alongside amber and pearl, meaning that it is derived from biological processes. In 1981, ammolite was officially recognized as a gemstone by the World Jewellery Confederation, coinciding with the beginning of commercial mining operations. In 2007, it was designated the official gemstone of Lethbridge, Alberta, highlighting its cultural significance in the region.
Ammolite is also known by other names, including aapoak, gem ammonite, calcentine, and Korite. The name “Korite” comes from a trademark used by Korite International, a leading mining company based in Alberta that specializes in the extraction of ammolite. Marcel Charbonneau and his business partner Mike Berisoff were the first to commercially develop and market ammolite doublets in 1967, later founding a company named Minerals Ltd to further their work.
Properties
The chemical composition of ammolite is variable, and in addition to aragonite, it may contain minerals such as calcite, silica, pyrite, and others. Trace elements such as aluminum, barium, chromium, copper, iron, magnesium, manganese, strontium, titanium, and vanadium are often present in the shell material, contributing to the complexity and beauty of the gemstone.
Ammolite has an orthorhombic crystal structure, with a hardness ranging from 3.5 to 4.5 on the Mohs scale, making it relatively soft compared to other gemstones. Its specific gravity varies from 2.60 to 2.85. The refractive index of Canadian ammolite, measured under sodium light (589.3 nm), ranges as follows: α 1.522, β 1.672–1.673, γ 1.676–1.679, and it is biaxial negative in optical character. Under ultraviolet light, ammolite may fluoresce a mustard yellow color, further adding to its allure.
The most striking feature of ammolite is its iridescence, which resembles the play of color seen in fine opals. This iridescence is primarily due to the microstructure of aragonite platelets, which interact with light to create brilliant interference colors. Unlike most other gemstones, where color results from light absorption by trace elements, ammolite’s colors are produced by the interference of light reflecting from multiple thin layers of aragonite.
The thickness of these layers determines the colors seen: thicker layers tend to produce reds and greens, while thinner layers produce blues and violets. Reds and greens are the most commonly observed colors because the thinner, more delicate layers responsible for blues are more prone to damage.
When ammolite is first extracted, its colors may appear muted or less dramatic. Proper polishing and, in some cases, additional treatments are required to reveal its full potential and vibrant array of colors. These processes help enhance the iridescence, making ammolite a truly breathtaking gemstone suitable for various types of jewelry.
Ammolite
Origin
Ammolite is derived from the fossilized shells of ammonites, specifically species such as Placenticeras meeki and Placenticeras intercalare, as well as, to a lesser extent, the cylindrical baculite species Baculites compressus. Ammonites were cephalopods, similar to modern-day squids and octopuses, that lived in the warm, shallow seas of the Late Cretaceous period. These creatures became extinct around the same time as the dinosaurs, marking the end of the Mesozoic era.
The ammonites that would eventually form ammolite lived in a prehistoric inland sea that covered much of what is now North America. This region, known as the Western Interior Seaway, was bordered by the Rocky Mountains. When the ammonites died, their shells settled to the seafloor, where they were buried under layers of bentonitic mud that eventually transformed into shale.
Many gem-quality ammonite fossils are found within siderite concretions. These sediments played a crucial role in preserving the aragonite layers of the shells, preventing them from converting to calcite over millions of years.
Today, the majority of ammolite is found in southern Alberta, Canada, with mining operations primarily taking place along the St. Mary River and other nearby areas. The unique geological conditions of this region have allowed ammolite to form and be preserved, making it one of the few places in the world where this beautiful gemstone can be sourced.
Uses in Jewelry and Symbolism
Ammolite is highly prized for its unique appearance and rarity, and it has become a popular gemstone for use in jewelry. Due to its relatively low hardness, ammolite is often fashioned into doublets or triplets to enhance its durability. A doublet consists of a layer of ammolite backed with another material, usually shale or black onyx, to provide stability and protection. A triplet includes an additional cap of synthetic quartz or spinel to safeguard the ammolite from scratches and enhance its brilliance.
The vibrant colors of ammolite have led to its association with positive energy, prosperity, and luck. In Feng Shui, ammolite is often regarded as an “influence stone,” believed to enhance the flow of energy (or “chi”) in the environment. Its multi-colored iridescence is thought to represent the harmony of all elements, making it a popular choice for those seeking to bring balance and well-being into their lives.
Care and Maintenance
Due to its relatively soft nature, ammolite requires special care to maintain its beauty. It is advisable to avoid exposing ammolite jewelry to harsh chemicals, extreme temperatures, or prolonged exposure to water. Cleaning should be done using a soft, damp cloth, and the gemstone should be stored separately from harder stones to prevent scratching. By taking proper care, the stunning iridescence of ammolite can be preserved for generations.
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