Ammolite

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Ammolite
Chemical composition CaC03 with trace elements
Crystal system Orthorhombic
Habit Fractured and non-fractured flat layers
Fracture Parting along layers
Hardness 3.5
Refractive index 1.525 - 1.670
Birefringence 0.135 - 0.145
Specific gravity 2.60 - 2.85
Lustre Vitreous to resinous
Triangular Ammolite Cabochon; Photo courtesy of Barbra Voltaire


Ammolite is the iridescent gem variety of a unique fossil ammonite, currently excavated only in southern Alberta, Canada. Ammonites are an extinct marine animal that first appeared 400 million years ago and became extinct at the end of the Cretaceous Period, 65 million years ago.
Natural ammolite has a hardness of 3.5, but is most often sold as a doublet or triplet in order to protect the gem material. Natural stones are often impregnated with an epoxy as a treatment to strengthen the ammolite.
Color comes from interference of light, and it is dependent on the thickness of the layers of aragonite. From thickest to thinnest: red, green, blue, and purple.
The color play is a result of iridescence (interference).

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