Topaz is a precious gemstone known for its bright colours. The stone may also be heat treated or irradiated to change its colour. Imperial topaz is the light brown to pink colour topaz found in nature rather than treated. Mystic topaz, also known as Mercury Mist, Aztec or Azotic topaz, is part of a family of topaz with a multicolour shine or borealis inside it.
History of Natural Topaz
The word topaz is believed to come from the Sanskrit word meaning "fire" or the Greek word Topazos meaning "to seek". Topaz is a clear and bright stone that ranges from red, to orange, to peach, pink, gold, yellow brown and clear. It can also be found in pale blue. Red and pink topaz was used in jewellery for 18th century imperial Russian tsarinas. It can be mistaken for a diamond but has a hardness of only eight. Topaz is a traditional gift for November births and the fourth, 19th and 23rd year of marriage.
Mineral Makeup of Topaz
Topaz is a fluorine-based aluminium fluorite silicate. The mineral can grow to very large sizes. The gem occurs naturally in rhyolite and granite cavities and high temperature veins. It can be found with tourmaline and cassiterite.
Heat and Irradiation
Most blue topaz is irradiated then heated to produce varying shades of blue. This process does not work on all stones.
In the 1990s, a new process was developed to deal with large quantities of clear topaz that would not keep the blue colour when irradiated and heated. A metallic layer is bonded to the bottom side of the gem at the molecular level. This creates several variations including pink, brown, green and blue topaz. These are known as Mystique or Mystic topaz. The variations create a borealis or multicolour shine inside the stone.
Mercury Mist Topaz
Mercury Mist topaz is a marketing term for a variation of Mystic topaz. This type of topaz has a blue to brown range with a rainbow borealis inside.