Rock Identifier
Ammolite (Ammolite (Biogenic Aragonite with trace elements; fossils of Placenticeras meeki and Placenticeras intercalare)) — mineral
mineral

Ammolite

Ammolite (Biogenic Aragonite with trace elements; fossils of Placenticeras meeki and Placenticeras intercalare)

Hardness: 3.5-4.5 (Mohs scale); Color: Iridescent play-of-color (red, green, blue, yellow); Luster: Vitreous to resinous; Crystal structure: Orthorhombic (aragonite); Specific Gravity: 2.60–2.85.

Hardness
3
Color
Iridescent play-of-color (red, green, blue, yellow)
Luster
Vitreous to resinous
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Physical properties

Hardness: 3.5-4.5 (Mohs scale); Color: Iridescent play-of-color (red, green, blue, yellow); Luster: Vitreous to resinous; Crystal structure: Orthorhombic (aragonite); Specific Gravity: 2.60–2.85.

Formation & geological history

Formed from the fossilized shells of Upper Cretaceous ammonites (approx. 70-75 million years ago). The shells were buried in the Bearpaw Formation under layers of bentonite, which prevented the aragonite from converting to calcite and preserved the iridescent layer.

Uses & applications

Primarily used in jewelry as gemstones (often as doublets or triplets due to softness) and high-end collector specimens. It is one of the few biogenic gemstones.

Geological facts

Ammolite was granted official gemstone status by the World Jewellery Confederation (CIBJO) in 1981. It is the official gemstone of the Province of Alberta, Canada.

Field identification & locations

Identify by its 'dragon skin' pattern (fractured mosaic) and intense iridescence that changes color as the stone is rotated. It is almost exclusively found in the Bearpaw Formation along the eastern slopes of the Canadian Rockies in Alberta.

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