Color is the most important characteristic of gems. There are terms to describe a color and nominations for top colors , some as imperial green for Emerald, pigeon blood for Ruby and cornflower blue for Sapphire.

Gemstones are found in many parts of the world. The attached mining map gives a roughly indication of the main deposits.

Friedrich Mohs set up a comparison scale using ten minerals of different degree. Each gemstone can scratch the softer one and the same hardness will scratch each other.

Stones with the hardness below 7 must be handled carefully when being worn and stored.

For more security for the gemstone buyer the following Nomenclature protect against a wrong name and improper evaluation of goods. RAL A5/A5E Guidelines for Precious Stones, Gemstones, Pearls and Corals for Germany. International regulated through the CIBJO (Confèderation Internationale de la Bijouterie, Joaillerie, Orfévrerie des Diamants, Perles, et Pierres). In the United States, the Federal Trade Commission (FTC). For Italy UNI (Ente Nazionale Italiano di Unificazione) n.10245,1993.