This week I've chosen a gemstone that I've only recently found out about, it's arguably one of the rarest gemstones on earth and is mainly sourced along the eastern slopes of the Canadian Rockies. It was only in 1981 that the CIBJO declared it an official variety of coloured gemstone. This beautiful gemstone is Ammolite.
Ammolite joins a small group of organic gemstones which includes amber, coral, jet and pearl and is primarily made up of the same mineral that makes up nacreous pearls. It typically occurs in shades of red and green that play across the stone in a similar way to opals.
Ammolite comes from the fossil shells of ammonites (hence the name!) and so is a very thin layer. It is for this reason that ammolite is usually impregnated with a clear resin before it's cut. The layer is very often fractions of a millimetre thick and so most gemstones set in jewelllery are composite stones. This means that the ammolite layer is adhered to a darker material, usually the mother stone or black onyx. This is known as a doublet, whereas a triplet will have a clear layer on top, most often synthetic spinel or synthetic quartz. This is a common treatment for opal too