Ammolite

Ammolite is one of the rarest, most visually spectacular, and most deeply fascinating biogenic gemstones on the planet. It is not a mineral born of cooling magma or intense underground pressure, but a biological relic of the Late Cretaceous period. It is the incredibly preserved, vividly iridescent, fossilized shell of ancient, extinct marine mollusks known as ammonites.

Officially recognized as a gemstone by the World Jewellery Confederation (CIBJO) only in 1981, Ammolite is a uniquely North American treasure. While ammonite fossils are common worldwide, the specific, intensely colorful, gem-quality material known as Ammolite is mined almost exclusively from a single, highly restricted geological layer in southern Alberta, Canada, known as the Bearpaw Formation.

Formation & Geology

To understand Ammolite, one must travel back 70 to 75 million years ago to the Western Interior Seaway, a massive, shallow ocean that split the North American continent in half. This warm sea was teeming with ammonites—squid-like predators that built tightly coiled, chambered shells made of aragonite (the exact same calcium carbonate mineral that makes up modern pearls).

When these creatures died, their shells sank into the thick, oxygen-poor, bentonite mud at the bottom of the sea. This specific mud sealed the shells perfectly, preventing them from dissolving or being crushed. Over millions of years, as the Rocky Mountains were pushed upward, the sea dried, and the mud turned into shale. The immense tectonic pressure compressed the microscopic layers of aragonite in the shells, but incredibly, the original mineral was not replaced.

Physical Characteristics

Ammolite is primarily composed of aragonite (CaCO₃), with trace amounts of silica, pyrite, and other minerals from the surrounding shale. It has a hardness of 3.5 to 4.5 on the Mohs scale.

However, its most critical physical characteristic is its microscopic structure. The aragonite in the shell is arranged in millions of incredibly thin, stacked, transparent plates or flakes. This structure gives Ammolite perfect micaceous cleavage, meaning it is incredibly fragile and will easily peel apart into thin layers if handled roughly or exposed to very dry air.

The phenomenon that makes Ammolite famous is its extreme iridescence. This is not caused by pigment, but by light interference. When light enters the tightly compressed, stacked aragonite plates, it bounces around and exits in specific wavelengths depending on the thickness of the layers. Thicker layers reflect vibrant reds and greens (the most common colors), while thinner, more highly compressed layers reflect the much rarer blues, purples, and violets. A high-quality Ammolite cabochon will flash the entire spectrum as it is turned in the light, resembling a fiery opal.

Gemology & Uses

Because the iridescent layer on an ammonite fossil is incredibly thin (often less than a millimeter) and highly prone to flaking (a process called “spalling”), cutting Ammolite for jewelry is exceptionally difficult.

To make it wearable, lapidaries almost always treat Ammolite. They stabilize the porous, flaky fossil by impregnating it under vacuum with clear, hard epoxy resin. Most commercial Ammolite is sold as a “doublet” or “triplet.” In a doublet, the fragile Ammolite layer is glued to a hard, dark backing stone (usually black shale or onyx) to provide strength and intensify the colors. In a triplet, a clear, domed cap of hard synthetic spinel or quartz is glued over the top of the Ammolite to protect it from scratching and magnify the iridescent flashes.

Metaphysical Properties

In the metaphysical community, Ammolite is revered as a stone of incredible ancient wisdom, grounding, and explosive, transformative energy. Because it is a fossil, it is strongly connected to the earth and the root chakra, believed to anchor the user during times of chaotic change.

However, its most famous use is in Feng Shui. Termed the “Seven Color Prosperity Stone,” Feng Shui masters believe the spiral shape of the ammonite shell perfectly mimics the coiled, swirling path of universal life force (chi). The brilliant, fiery, iridescent colors are thought to represent all five elements (fire, earth, metal, water, wood), making Ammolite an incredibly powerful talisman for attracting wealth, promoting robust health, and harmonizing the energetic flow of any home or business.