What is Ammolite? Properties, Uses

Ammolite is a stunning iridescent gemstone formed from the fossilized shells of ammonites, which were extinct cephalopods related to the modern nautilus and octopus.

Ammolite: Iridescent Ammonite Fossils

Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America. Ammolite is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral contained in nacre, with a microstructure inherited from the shell. It is one of few biogenic gemstones; others include amber and pearl.

Rare Giant Natural Ammolite From Alberta, Canada.

Over time, mineralization processes occurred, transforming the aragonite, the primary mineral in ammonite shells, into a mixture of minerals known as aragonite and calcite. The resulting material is what we now call ammolite. The gemstone is valued for its vibrant and iridescent colors, which are a result of the interference and diffraction of light as it passes through the layers of the fossilized shell.

Ammolite iridescent opal-like play of color is shown in fine specimens, mostly in shades of green and red; all the spectral colors are possible, however. The iridescence is due to the microstructure of the aragonite: unlike most other gems, whose colors come from light absorption, the iridescent color of ammolite comes from interference with the light that rebounds from stacked layers of thin platelets that make up the aragonite.

Properties of Ammolite

Composition: Ammolite is composed mainly of aragonite, which is a carbonate mineral belonging to the aragonite group. The aragonite forms the intricate layers in the fossilized shell of ammonites. Additionally, small amounts of other minerals may be present, contributing to the gemstone's iridescence.

Color: Ammolite is renowned for its vibrant and iridescent colors, which can include shades of red, green, blue, and violet. The play of colors is a result of the interference and diffraction of light as it passes through the layers of aragonite and calcite.

Transparency: Ammolite is typically translucent to opaque. The layers of aragonite and calcite contribute to its optical properties, including the play of colors, but also affect its transparency.

Luster: The luster of ammolite is generally vitreous, giving it a glassy appearance when polished.

Streak: Ammolite does not have a streak color as it is not used for streak testing. Streak testing is more applicable to minerals with hardness sufficient to leave a streak on a streak plate.

Hardness: Ammolite has a relatively low hardness of around 3.5 to 4.5 on the Mohs scale. This makes it susceptible to scratching, and care should be taken in handling and wearing ammolite jewelry.

Specific Gravity: The specific gravity of ammolite varies but is generally around 2.6 to 2.8. Specific gravity is a measure of density, indicating how heavy a mineral is compared to an equal volume of water.

Solubility: Ammolite is not readily soluble in water. However, like many carbonate minerals, it can be affected by acids, which can lead to effervescence due to the release of carbon dioxide.

Fluorescence: Ammolite may exhibit fluorescence under ultraviolet (UV) light. The fluorescence can vary in color and intensity.

Pleochroism: Pleochroism refers to the ability of a mineral to exhibit different colors when viewed from different angles. Ammolite may display pleochroism, contributing to its dynamic play of colors.

Refractive Index: The refractive index of ammolite varies, but it generally falls within the range of 1.52 to 1.68. The refractive index influences how light is bent or refracted as it enters and exits the gemstone.

Inclusions: Inclusions in ammolite can include remnants of the original ammonite shell structure, mineral inclusions, or other organic material. These inclusions can add character to individual gemstones but are typically not as prominent as the overall play of colors.

Giant Natural Ammolite from Alberta, Canada.

Ammolite Occurrence and Distribution

Ammolite, the iridescent gemstone formed from fossilized ammonite shells, boasts a unique and limited distribution across the globe. While its formation process requires specific geological conditions, it's fascinating to explore the locations where these mesmerizing gems have been unearthed.

Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meeki and Placenticeras intercalare, and (to a lesser degree) the cylindrical baculite, Baculites compressus. Ammonites were cephalopods, that thrived in tropical seas until becoming extinct along with the dinosaurs at the end of the Mesozoic era.

Southern Alberta, Canada: The undisputed champion of ammolite production, boasting the Bearpaw Formation, an expansive geological unit spanning roughly 1.5 million square kilometers. This formation, dating back to the Late Cretaceous period, offers the ideal combination of marine sediments, organic matter, and silica-rich fluids, fostering the creation of exceptional ammolite deposits.

Montana, USA: The Judith Basin in Montana harbors promising ammolite deposits, sharing geological similarities with the Bearpaw Formation. While less extensively explored, it demonstrates the potential for further discoveries in neighboring regions.

Madagascar: The Mahajanga Province in Madagascar has revealed exciting ammolite deposits in recent years. While the quality and quantity can vary compared to Canadian sources, ongoing explorations might unveil hidden gems.

Canadian Ammolite Ammonite Freeform

Uses and Cultural Significance

Ammolite is primarily used in the creation of unique and vibrant jewelry. Its distinctive play of colors and fossilized origin make it a sought-after gemstone for various purposes. Here are some common uses of ammolite:

Jewelry:

Gemstone Cabochons: Ammolite is often cut and polished into cabochons, showcasing its colorful play of colors. These cabochons are then set into jewelry, such as rings, earrings, pendants, and bracelets.

Carvings and Artistic Pieces: Skilled artisans may carve intricate designs into ammolite, creating one-of-a-kind artistic pieces that highlight the gemstone's unique properties.

Collector's Items:

Ammolite's rarity and the geological story it tells make it a sought-after item for gemstone collectors. High-quality specimens with vibrant colors and unique patterns are particularly valued.

Spiritual and Metaphysical Uses:

Some people believe in the spiritual and metaphysical properties of gemstones. Ammolite, with its connection to ancient marine life and vibrant energy, is believed by some to bring balance, prosperity, and well-being. It is also thought to enhance the flow of chi (energy) in feng shui practices.

Custom Designs:

Jewelry designers and lapidaries may use ammolite in custom designs, combining it with other gemstones or metals to create unique and personalized pieces.

Symbolic Jewelry:

Ammolite's connection to ancient marine life and its place in the fossil record make it a symbolic choice for jewelry. It can represent longevity, the passage of time, and the interconnectedness of life.

Cultural and Indigenous Art:

Indigenous Connection: The indigenous peoples of the region where ammolite is found, particularly the Kainai Nation of the Blackfoot Confederacy, hold a deep reverence for the gemstone. For centuries, they have regarded ammolite as a sacred stone with cultural significance, reflecting their connection to the land and its ancient history.

Educational and Scientific Displays:

Museums and educational institutions may use ammolite specimens in displays and exhibits related to paleontology, geology, and the history of life on Earth. The gemstone's fossilized origin and vibrant colors can capture the attention of visitors.

Corporate Gifts and Awards:

High-quality ammolite pieces are sometimes used as corporate gifts or awards due to their uniqueness and aesthetic appeal.

Ammolite jewelry (rings, earrings, pendants)

Conclusion

Ammolite stands as a testament to the Earth's rich geological past, preserving the beauty of prehistoric seas in a dazzling array of colors. From its origins in the depths of the ocean to its transformation into a cherished gemstone, ammolite continues to captivate and inspire all who encounter its enigmatic beauty. As we marvel at the iridescent hues of this remarkable gemstone, we are reminded of the enduring legacy of life on Earth and the timeless allure of nature's wonders.