Topaz is a highly priced valuable gemstone. It comes in a crystallite form and is a kind of mineral of silicate origin. Most people know topaz as a yellow gemstone, and in jewelry it is seen most commonly in a range of tints from pale yellow to rich brown. The most desirable shade is a medium brown with a tint of red, a subtle color not found in any other gemstone. Pink topazes are also much admired, the more so the deeper their color. They are very rare in nature; practically all are produced by a carefully controlled heat treatment of brown stones. A topaz color seen in jewelry as blue is enhanced to become blue, because few blue topazes have a sufficiently deep color. Most are paler than aquamarines and like these can have a greenish tint. Most common and also less valuable is completely pure, colorless topaz. Colored topazes have been very popular from the sixteenth century onward, and have often been worn in exquisite settings as necklaces, earrings, brooches or entire suites. Being hard, they take an excellent polish and display a fair luster. Their depth of color varies from stone to stone, so that it is no simple matter to match a number of stones exactly.