Ammolite

Ammolite is an unusual gemstone, consisting of the iridescent coating of ammonite fossils. It largely comes from Canada, with a smaller source in Colorado.

It is quite a rare find, and when cut for jewellery usage, is almost always stabilised with resin to form a doublet or triplet.

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Appearance, Uses and History

Ammolite is a gemstone comprised of the fossilised shells of Ammonites. It is comprised of Aragonite, sometimes with mild impurities of other minerals. Light refracts within the layers of Aragonite, causing bright flashes of colour.

Ammolite is exclusively used for two things – jewellery making, and fossil/mineral specimens.

Several species of Ammonite seemed to have gained this gorgeous colour – Placenticeras meeki, and Placenticeras intercalare being the two most common. Another is Baculite compressus; a straight member of the Ammonitida family.

Red and greens are the most common colours shown but there are many other possibilities.

A single company, Korite, controls around 90% of all gem quality Ammolite. Generally speaking, the deeper the mine, the higher quality the specimens – at 15 meters deep it is often cracked and crackled. At  a depth of 20 meters, there is ‘sheet Ammolite’, a higher quality, less fractured material.

There is no standardised grading system for Ammolite, but the system used by Korite is quite detailed.

Ammolite should not be confused with other iridescent Ammonites. There are often specimens from Madagascar missold as Ammolite. While they do show iridescent patches of colour as a result of the same phenomenon, they are not a gem grade.


Locales

Almost all Ammolite on Earth is found in the Bearpaw formation, which stretches from Alberta to Saskatchewan in Canada, along the eastern slopes of the Rocky Mountains.

However, there are small deposits elsewhere, including Colorado and Utah.


Mineralogy

Chemistry
CaCO3, a polymorph of Aragonite.
Colours and Variations
Grey, green, or brown usually, with a bright iridescence which is usually red, green, yellow, blue, or orange.
Streak
Luster
Silky to vitreous, takes a good polish.
Fracture
Uneven to granular
Crystal habit
Mohs hardness
3.5 – 4.5
Specific Gravity
Around 2.7, although this does vary.
Easiest testing method
Locale, visual inspection.
Common Treatments
It tends to be stabilised with clear epoxy or another clear resin.
Almost all Ammolite is polished and made into a doublet – a backed cabochon. Some pieces are made into triplets, if they are too thin.

Photos of Ammolite

Ammolite from Placenticeras fossil ammonite (Bearpaw Formation, Upper Cretaceous, 70-75 Ma; mine in St. Mary River Valley, Alberta, Canada) 5 (40448036885)
Ammolite from Placenticeras fossil ammonite, Alberta
Ammolite from Placenticeras fossil ammonite (Bearpaw Formation, Upper Cretaceous, 70-75 Ma; mine in St. Mary River Valley, Alberta, Canada) 3 (32180813094)

BLW Ammolite ammonite (1)
Iridescent Ammonite Fossil
Placenticeras meeki Musée des Confluences 18102015 4

Placenticeras meeki Musée des Confluences 18102015 5
Ammolite from Placenticeras fossil ammonite (Bearpaw Formation, Upper Cretaceous, 70-75 Ma; mine in St. Mary River Valley, Alberta, Canada) 10 (40630261644)
Placenticeras meeki Musée des Confluences 18102015 1

Hazards and Warnings

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis.

When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.


Translations

Arabic:

  • أموليت

Hindi:

Portuguese:

Bengali:

Indonesian:

  • ammolit

Punjabi:

English:

  • ammolite
  • calcentine
  • korite
  • aapoak

Italian:

Russian:

French:

Japanese:

  • アンモライト

Spanish:

  • Ammolita
  • Calcentita

German:

  • Ammolit
  • Ammolith
  • Calcentit

Korean:

  • 암모 올 라이트

Thai:

Gujurati:

Mandarin and Traditional Chinese:

  • 斑彩石

Urdu:


Further Reading / External Links