Topaz called “London blue”, natural and transparent, cushion cut, 5.27 carats,

Topaz : Topaz is a silicate mineral of aluminium. Imperial topaz is yellow, pink (rare, if natural) or pink-orange. Brazilian Imperial Topaz can often have a bright yellow to deep golden brown hue, sometimes even violet. Many brown or pale topazes are treated to make them bright yellow, gold, pink or violet colored. Naturally occurring blue topaz is quite rare. Typically, colorless, gray or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue.
Cushion cut : The cushion cut is a rather rare cut that could be defined as a combination between the antique Old Mine Cut and the modern oval cut.
Carat : The carat (ct) is a unit of mass equal to 2 g. Carat is used for measuring the weight of gemstones.