Besides diamonds, colored gemstones have always been popular for jewelry. Sapphires, rubies, and emeralds used to be classified as precious gemstones whereas, all others were considered semi-precious. Precious and semi-precious gem designations are not used in the gem and jewelry industry any more since they are not accurate to describe the value, rarity or availability of a particular gem type. Gemstones are rare in nature and are often enhanced in addition to faceting or shaping; through treating with heat, radiation, oils, or waxes to hide minor blemishes or to enhance the color. These processes are all considered standard practice in the gem business. Some types of beautiful natural gems that have not been enhanced can be worth as much as, or more per carat than a diamond of comparable quality, and often come with a certificate of authenticity from an independent gem laboratory.