Ammolite

Ammolite is the pearly, iridescent layer of the shells of ammonites that lived about 70–75 million years ago. An ammonite was an extinct sea animal, a distant relative of the squid. Because thin layers of aragonite in the shell reflect light by interference, it shows red, green and, more rarely, blue and purple. Gem-quality ammolite in commercial quantities has only been found in the province of Alberta in southern Canada. The layer is thin and soft, so most stones are assembled, such as doublets and triplets.

Jewellery: used in every kind of jewellery, such as rings, necklaces, earrings and brooches. Because the layer is thin and soft, most stones are made as doublets or triplets; in a triplet the ammolite sits between a shale backing below and a cap of quartz or synthetic spinel above. Decoration and collecting: complete ammonite fossils and unworked pieces are also sought after for collections and decoration. Science: the microstructure of the shell, and colour produced by light interference, are of interest to gemology and palaeontology.

It has a hardness of 3.5–4 on the Mohs scale. A fingernail cannot scratch it, but a steel knife can. Its specific gravity is 2.76–2.84 g/cm³.

Its best-known localities: St. Mary River valley (between Lethbridge and Magrath), Alberta, Canada; Kainai (Blood) Reserve, Alberta, Canada.

It shows rainbow colours: red and green are the commonest, blue is rare and purple very rare. The colour changes as you tilt the stone; in a mainly red stone it shifts through orange and yellow to green. It is soft (Mohs 3.5): fluorite scratches it, calcite does not. In most rough pieces the coloured areas look like a mosaic of panes set off by thin healed fractures; some pieces show rare “suture” patterns that mimic the internal structure of the ammonite. Doublets and triplets: a thin layer of ammolite is glued onto shale or another backing (doublet); in triplets a cap of clear quartz or synthetic spinel is added on top. These are not natural single-piece stones and must be sold as such.

On the “street to diamond” value ladder it sits on step 6 of nine: Fine ornamental and collector stone. The variety and brightness of the colours matter most for ammolite: the more colours a stone shows, the higher its grade; the full spectrum, and especially blue and purple, is most sought after, while stones that show only red or brown are worth less. Sharp, bright colours that do not go dark from some angles, and the rare suture patterns that recall the ammonite shell, add value. Whether a stone is a solid piece or a doublet or triplet, and whether it has been impregnated with resin (stabilised), must be disclosed; untreated solid stones are generally worth more.

The Blackfoot people call ammolite and ammonite fossils “iniskim”, the “buffalo stone”; the stone is believed to bring luck in the buffalo hunt and is used in ceremonies and prayers. Ammonite fossils, the raw material of ammolite, have been the subject of other beliefs through history: in medieval Europe they were taken for petrified snakes, some Europeans credited them with power against witchcraft, and Hindus regard ammonites from Nepal’s Gandaki River as a concrete manifestation of Vishnu. Some feng shui practitioners in Asia say that ammolite, because of its seven colours, is a “prosperity stone” that supports the flow of chi and brings wealth, wisdom and growth. The colours of ammolite are a physical result of aragonite layers reflecting light by interference; there is no scientific evidence that the colours represent an energy or a benefit such as wealth or wisdom, bring luck in hunting, or protect anyone. Ammonite fossils and ammolite hold sacred meaning for the Blackfoot and other Indigenous peoples of North America, and that meaning should be mentioned with respect. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.