A gem is generally defined as any mineral that is highly prized for its beauty, durability, and rarity, is used for personal adornment, and has been enhanced in some manner by altering its shape—usually by cutting and polishing. A wider definition includes a few rocks, such as obsidian, and a few organic substances, such as amber (a fossilized resin). By far the majority of gems, however, are cut from the crystals of minerals. Precious metals are not considered to be gems, nor are items carved from minerals but not used for personal adornment, such as figurines, bowls, or vases.