How Is Ammolite Formed?

The story of Ammolite begins more than 70 million years ago, when much of present-day Alberta lay beneath a vast inland sea known as the Western Interior Seaway.

This warm, shallow sea stretched across the center of North America and was home to a diverse range of marine life, including the ammonites whose fossilized shells would eventually become Ammolite.

The formation of Ammolite required an extraordinary combination of biological, geological, and environmental conditions that occurred over millions of years.

Life in an Ancient Sea

Ammonites were marine animals closely related to modern squid, octopuses, and nautiluses. They possessed coiled shells composed primarily of aragonite, a mineral also found in many modern shells.

For millions of years, ammonites thrived throughout the Western Interior Seaway. When they died, their shells sank to the seafloor where most would normally break down, dissolve, or be destroyed.

Only a small number experienced the conditions necessary for long-term preservation.

Preserving the Shell

In most fossilization processes, the original shell material is gradually replaced by other minerals.

What makes Ammolite unusual is that portions of the original aragonite shell survived. Layers of sediment buried the shells, helping protect them from physical and chemical destruction while pressure from accumulating sediments compacted the surrounding rock.

Over millions of years, the shell became fossilized while retaining much of its original microscopic structure.

The Origin of Ammolite's Colours

The preserved shell is made up of countless microscopic layers of aragonite stacked on top of one another.

When light strikes these layers, it reflects back at different wavelengths. This causes interference effects that produce the vibrant colours associated with Ammolite.

The thickness and arrangement of the layers determine which colours appear. Slight differences in shell structure can dramatically alter the resulting colour display.

This is why one stone may show mostly reds and greens, while another displays blues, purples, or a broad spectrum of colours.

Why Southern Alberta?

Ammonites lived throughout the world's oceans, yet gem-quality Ammolite is found almost exclusively within the Bearpaw Formation of Southern Alberta.

Scientists believe a unique combination of sediment composition, pressure, mineral chemistry, and burial conditions allowed the shell material in this region to survive in exceptional condition.

Without these conditions, the delicate aragonite layers responsible for Ammolite's colours would likely have been destroyed long ago.

Seventy Million Years in the Making

The formation of Ammolite cannot be recreated on a human timescale.

Each gemstone represents the preserved remains of an animal that lived during the age of dinosaurs and underwent millions of years of fossilization before eventually being discovered.

This extraordinary journey—from a living marine animal to a brilliantly coloured gemstone—is what makes Ammolite one of the most fascinating and unique gemstones on Earth.