Ammolite
Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral contained in nacre, with a microstructure inherited from the shell. It is one of few biogenic gemstones; others include amber and pearl. In 1981, ammolite was given official gemstone status by the World Jewellery Confederation (CIBJO), the same year commercial mining of ammolite began. It was designated the official gemstone of the City of Lethbridge, Alberta in 2007.
| Ammolite | |
|---|---|
Unprocessed sample of ammolite; a "dragon skin" pattern is apparent | |
| General | |
| Category | fossilized, mineralized Ammonite shell |
| Formula (repeating unit) | CaCO 3 aragonite polymorph, with minor amounts of calcite, pyrite, silica, and other impurities |
| Identification | |
| Color | Gray to brown, can be radiant blue, with primarily red to green iridescence. |
| Cleavage | no true cleavage |
| Fracture | uneven to granular |
| Mohs scale hardness | 3.5 - 4.5 |
| Luster | greasy to dull |
| Specific gravity | usually about 2.70 (varies with mineral content) |
| Polish luster | vitreous |
| Optical properties | anomalous aggregate reaction |
| Refractive index | usually 1.52 - 1.68 (varies with mineral content) |
| Birefringence | 0.135 - 0.145 |
| Pleochroism | none |
| Ultraviolet fluorescence | variable |
Ammolite is also known as aapoak (Kainah for "small, crawling stone"), gem ammonite, calcentine, and korite. The latter is a trade name given to the gemstone by the Alberta-based mining company Korite. Marcel Charbonneau and his business partner Mike Berisoff were the first to create commercial doublets of the gem in 1967. They went on to form Ammolite Minerals Ltd.