Ammolite Mining
Ammolite is a rare and valuable opal-like organic gemstone found primarily in south eastern Alberta. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral that makes up nacreous pearls. It is one of a few biogenic gemstones; others include amber and pearl. In 1981, Ammolite was given official gemstone status by the World Jewelry Confederation, the same year commercial mining of ammolite began. It was designated the official gemstone of the Province of Alberta in 2004 and the official gemstone of the City of Lethbridge in 2007.
Commercial extraction is mechanized but fairly basic: pits are dug up to 400 ft. deep and the excavated material is screened for its potential gem contents. The pits are further examined by hand, and commercial production. Approximately 50% of the ammolite mined is suitable for jewelry.
The ammolite deposits are stratified into several layers: the shallowest of these layers, named the “K Zone”, lies some 15 meters below the surface and extends 30 meters down. The ammolite within this layer is covered by siderite concretions and is usually cracked—this is the crush material. It is the most common (and some consider) the least valuable of the Ammolites. Beginning twenty meters below the crush material is the “Blue Zone”; ammolite from this zone, which extends 65 meters, is usually compressed with a thin layer of pyrite rather than siderite concretions. This is the sheet material; due to its depth it is rarely mined. It is also much less fractured, and therefore the more valuable type of ammolite.