Mined from both host rock and alluvial deposits, its unique crystal structure makes topaz a hard and dense gemstone. Because of this, pure colorless topaz has often been mistaken for diamond. Weighing 1,680 carats, the huge Braganza gemstone mounted into the Portuguese crown jewels was originally thought to be a diamond—in fact it is a beautiful clear topaz.
A hydrous aluminum fluorosilicate, topaz is usually formed in granitic pegmatites and in quartz veins.
