This category is for information about gemstones and their properties. Gemstones are generally regarded as: Polished fragments of 'precious' and 'semi-precious' minerals, used for decorative purposes. Examples of Precious Stones: Diamonds / Sapphires / Rubies / Emeralds Examples of Semi-Precious Stones: Topaz / Garnet / Spinels. Examples of Other stones used as gems: Jade / Agate / Opal