Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It is the birthstone of the month November. It crystallizes in the orthorhombic group and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage, meaning that gemstones or other fine specimens have to be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4–3.6, and a vitreous luster. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may be made white, gray, green, blue, pink or reddish-yellow and transparent or translucent.
Many 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: this shall be the first row." However, since these translations as topaz all derive from the Septuagint translation topazi[os], which as mentioned above referred to a yellow stone that wasn't topaz, 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; pitdah is of unknown meaning, though scholars think it is related to an Assyrian word meaning flashed. There is a wide range of views among traditional sources about which tribe of the Israelites the stone refers to.
Yellow topaz is the traditional November birthstone, the symbol of friendship, and the state gemstone for the US State of Utah.