Topaz is a transparent gemstone which usually contains some inclusions. They can be the liquid and gaseous inclusions which are in the dacryoideous hollows. In topaz there can be cracks or cracks with gas-liquid inclusions in the form of veils. It is a durable stone, has a sufficient hardness and it is not scratched by the other stones. Topaz crystals quite often are very big; in 1964 in Ukraine dark blue crystals of topaz 100 kg each have been found.
As colour of topaz is seldom bright, it has a step cutting to show a stone in its best view. Colourless or weak-colored material often has a diamond facet to create a bright gemstone.
Topaz has a wide range of colours which depends on the impurities or painting substances. The most usual natural colours are yellow, yellowy-brown, orange-brown, pink-brown; and also there are sky-blue, bright Swiss dark blue and colourless stones. The most expensive and demanded colours are topaz of a sherry colour, imperial topaz (apricot or orange colour) and pink topaz (shades from light pink to violet-red).
Estimation of topazes
Topazes of very big sizes are found, but they have a high density and, like garnets, they weigh more than the other gems of the same size. The stone weight essentially influences its price. The prices for pink and imperial topazes are very high. The prices for yellow, brownish-orange, dark blue and colourless topazes are much lower.
Hardness 8 on Moos scale
Density from 3,49 to 3,57
Factor of refraction from 1,609 to 1,643
Crystal lattice: orthorhombic system. The majority of topaz crystals have the prism form; one end of the crystal has the wedge shape. They have a characteristic eight-side cross-cut section with grooves on the length of a stone.
Topazes are found in the volcanic rocks of pegmatite type and volcanic lavas or in the form of the alluvial pebble. They are often connected with the gold deposits.
Deposits of topazes: the Great Britain (Cornwall, Northern Ireland, Scotland), Afghanistan, Australia, Myanmar (Burma), Nigeria, Sri Lanka, Brazil, Pakistan, the USA, Russia.