Topaz is a silicate mineral of aluminium  and fluorine  with the chemical formula Al2SiO4(F, OH)². Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces. Pure topaz is colorless and transparent but is usually tinted by impurities; typical topaz is wine, yellow, pale gray or reddish-orange, blue brown. It can also be made white, pale green, blue, gold, pink (rare), reddish-yellow or opaque to transparent/translucent.

Etymology and historical and mythical usage

The name "topaz" is derived (via Old French: Topace and Latin: Topazus) from the Greek Τοπάζιος (Τοpáziοs) or Τοπάζιον (Τοpáziοn), the author of one of the first systematic treatises on minerals and gemstones, who 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.

any modern English translations of the Bible, including the King James Version mention Topaz in Exodus 28:17 in reference to a stone in the Hoshen: "And thou shalt set in it settings of stones, even four rows of stones: the first row shall be a sardius, a topaz, and a carbuncle (Garnet): this shall be the first row."

However, because these translations as topaz all derive from the Septuagint translation topazi, which as mentioned above referred to a yellow stone that was not topaz, but probably chrysolite, it should be borne in mind that topaz is not meant here. The masoretic text (the Hebrew on which most modern Protestant Bible translations of the Old Testament are based) has pitdah as the gem the stone is made from; some scholars think it is related to an Assyrian word meaning flashed.[citation needed] More likely, pitdah is derived from Sanskrit words (पीत pit = yellow, दह् dah = burn), meaning "yellow burn". Pliny says that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. The word topaz might be related to the Arabic word توباز which meant "the subject of the search" or Sanskrit word तपस् "tapas" meaning "heat" or "fire."

Source : Wikipedia