Topaz is a silicate mineral of aluminium and fluorine with the chemical formulaAl2SiO42. Topaz crystallizes in the orthorhombic system, and its crystals are mostly prismatic terminated by pyramidal and other faces. It is one of the hardest naturally occurring minerals and is the hardest of any silicate mineral. This hardness combined with its usual transparency and variety of colors means that it has acquired wide use in jewellery as a cut gemstone as well as for intaglios and other gemstone carvings.
Characteristics
Topaz in its natural state is a golden brown to yellow – a characteristic which means it is sometimes confused with citrine, a less valuable gemstone. A variety of impurities and treatments may make topaz wine red, pale gray, reddish-orange, pale green, or pink, and opaque to translucent/transparent. The pink and red varieties come from chromium replacing aluminium in its crystalline structure. Orange topaz, also known as precious topaz, is the conventional birthstone for November, the symbol of friendship, and the state gemstone of the U.S. state of Utah. Imperial topaz is yellow, pink or pink-orange. Brazilian imperial topaz can often have a bright yellow to deep golden brown hue, sometimes even violet. Many brown or pale topazes are treated to make them bright yellow, gold, pink, or violet colored. Some imperial topaz stones can fade on exposure to sunlight for an extended period of time. Blue topaz is the state gemstone of the US state of Texas. Naturally occurring blue topaz is quite rare. Typically, colorless, gray, or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue. Mystic topaz is colorless topaz which has been artificially coated via a vapor deposition process giving it a rainbow effect on its surface. Although very hard, topaz must be treated with greater care than some other minerals of similar hardness because of a weakness of atomic bonding of the stone's molecules along one or another axial plane. This gives topaz a tendency to break along such a cleavage plane if struck with sufficient force. Topaz has a relatively low index of refraction for a gemstone, and so stones with large facets or tables do not sparkle as readily as stones cut from minerals with higher refractive indices, though quality colorless topaz sparkles and shows more "life" than similarly cut quartz. When given a typical "brilliant" cut, topaz may either show a sparkling table facet surrounded by dead-looking crown facets or a ring of sparkling crown facets with a dull well-like table.
It is possible to synthesize topaz. However, naturally occurring topaz is so abundant that this is probably not economically viable.
Etymology
The name "topaz" is usually derived from the GreekΤοπάζιος or Τοπάζιον, from Τοπαζος, the ancient name of St. John's Island in the Red Sea which was difficult to find and from which a yellow stone was mined in ancient times; topaz itself was not really known before the classical era. Ancient Sri Lanka exported native oriental topazes to Greece and ancient Egypt, which led to the etymologically related names of the island by Alexander Polyhistor and the early Egyptians – "land of the Topaz". Pliny said that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. Alternatively, the wordtopaz may be related to the Sanskrit word तपस् "tapas", meaning "heat" or "fire".
Historical usage
Nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652. In the Middle Ages, the name topaz was used to refer to any yellow gemstone, but in modern times it denotes only the silicate described above. Many English translations of the Bible, including the King James Version, mention topaz. However, because these translations as topaz all derive from the Septuagint translation topazi, which referred to a yellow stone that was not topaz, but probably chrysolite, topaz is likely not meant here.
Superstition
An English superstition also held that topaz cured lunacy. The ancient Romans believed that topaz provided protection from danger while traveling. During the Middle Ages, it was believed that attaching the topaz to the left arm protected the owner from any curse and warded off the evil eye. It was also believed that wearing topaz increased body heat, which would enable people to relieve a cold or fever. In Europe in the Middle Ages, topaz was believed to enhance mental powers.
