Pokhraj Gemstone is known as Topaz in English. Pokhraj is a much-valued gemstone, the chemical formula being Al2SiO4(F,OH)2. The esteemed gemstone variety is a wine-yellow Pokhraj, but the blue, pale green and pink varieties are also gemstone. A rose-pink variety is yellow stone changed by heating. These varieties exhibit dichroism. Pokhraj is a durable stone (Hardness 8) with some brilliance and considerable beauty.
In the jewellery trade, may stones have been called topaz, such as ‘Oriental topaz’ (yellow corundum). ‘Bohemian topaz’ is fluorspar and the true stone is called ‘Brazilian topaz’.
Pokhraj, usually found in the pegmatite and granites, are formed by pneumatolytic (high-temperature gaseous action) processes.
Good-quality Pokhraj is found in Singhbhum district, Bihar and in Bhandara district, Maharashtra. Pokhraj is found in the Kanyaluka area (Singhbhum district) is transparent and light blue in colour, while Pokhraj of the Kharsawan area (Singhbhum district) exhibits a light yellow colour. In Maharashtra, Pokhraj and dumortierite (sillimanite) have been found in quartz-kyanite rocks in the district of Bhandara.