Topaz, also called "Saxon diamond" (from the Saxons) with the orthorhombic crystallization system, is a mineral of the gemstone category with the chemical composition Al2SiO4(OH, F)2. Hydroxyl ions (-OH) can combine with different concentrations of fluorides, which results in the large number of varieties of topaz. Topaz by gamma-ray irradiation, electron bombardment. or heating changes colour to greenish-brown or reddish. Although it has a hardness of 8 it has a good cleavage (splits easily) which makes it difficult to process.
It occurs in the characteristic form of prismatic crystallization or as a lumpy mass. Frequently associated with beryl, tourmaline and apatite in an acidic granite or pegmatite magmatic rock, it can also be found in metamorphic gneissic rocks (Brazil). Other places where topaz has been found include the Czech Republic, Norway, Sweden, Japan, Mexico, the USA, Sri Lanka, Burma and Pakistan. In the past, topazes were found in Germany's Saxony on the Snail Mountain in the Vogtland from where polished topazes from the time of August the Hard are now kept in the "Green Room" in Dresden and the English Crown.
Topaz is frequently used as a valuable gemstone. The largest topaz found to date is a 271 kg crystal, and the largest worked (polished) topaz weighs 4.2 kg.
According to accounts by the Roman naturalist Plinius, the mineral's name comes from the island 'Topazos' in the Red Sea. In fact no topaz was found there, but olivine, with which it was confused. Another source of the name comes from a Sanskrit word tapas meaning 'fire'. In 1740 a white topaz was mounted in the Portuguese crown, it was named "Diamant de Braganza" and believed to be a diamond.