Ammolite

The ammolite is a decorative Pierre of origin Biogénique, of red-greenish aspect and iridescent. It comes exclusively from the east of the Rocky Mountains, with the Canada and the the United States. It is resulting from Fossile S of Ammonite S, of the Placenticeras of the geological formation of Bearpaw Shale. These fossils contain Aragonite, that is to say the component main thing of the Nacre.

She is considered an official gem by CIBJO since 1981, the year which saw beginning its commercial exploitation. In 2004 it was indicated the official gem of the Province of the Alberta, Canada. In Jewelry, the ammonite competes even with the Opale.

Chemical composition

Apart from the aragonite, this stone contains also Calcite, Pyrite or Silice. elements of trace like the Aluminum, the Barium, the Chromium, the Copper, the Iron, the Magnesium, the Manganese, the Strontium, the Titanium and the Vanadium are also detected.

Physical properties

The ammolite is in fact a very thin layer, which makes approximately 0,5 to 0,8 mm thickness. Usually one finds it with his matrix.

Its Cristallographie is orthorhombic. Its hardness is not very high, ranging between 4,5 and 5,5. Its relative density is between 2,6 and 2,85. The Index of refraction, measured on Canadian samples thanks to the light of Sodium, is: α 1,522; β 1,672 - 1,673; γ 1,676 - 1,679. Under rays Ultraviolet S, the ammonite emits a Fluorescence yellow color mustard.

Use

This stone was known Amerindian S of the tribe of the Pieds-Noirs (Blackfoot). They used it as ornament crowned for rites preceding hunting for the Bison, like with medical goals.

See too

the Pearl and the Amber, two other decorative stones biogenic.

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