Last week we discussed minerals and concluded they are divided into two groups, the silicate minerals with silicon and oxygen in different ratios, and the non-silicate minerals. Topaz, one of November’s two birthstones, is a silicate mineral with the chemical formula Al2SiO4(F,OH)2. Its name originates in St. John’s Island in the Red Sea, Τοπάζιος (Τοpáziοs) in ancient Greek. Topaz is a semi-precious gemstone.
Topaz comes in many colours and mystic topaz means that a colourless gem has been treated to give its surface a rainbow effect (see if you can find it in the picture!). It is transparent and an 8 on the Mohs scale of mineral hardness, with 7-10 being able to scratch the surface of glass, and 1-6 being damaged by a scratching knife along their surface. Diamond is the hardest at 10 and talc the softest at 1.
If you want to see huge topaz crystals in real life, there are many natural history museums around the world that have them in their collections. The largest cut gemstone is The American Golden Topaz of almost 22,900 carat or over 4.5 kg, whereas in 1986 a crystal weighing a whopping 5 tonnes (2 x 1.8 metres) was found in Brazil, a significant source of topaz. Smaller crystals have been found in many locations around the world.
It is enough to clean a topaz quickly under running water. Apparently it’s also beneficial to place it in direct sunshine for a short while, to “recharge it”. Regardless of cleaning procedure, remember it can crack when forced through large temperature changes or when it is slammed hard against another object.
Topaz is the birthstone of November in both the U.S. and U.K.