Known in the trade as 'London' blue topaz, a designation which refers to the deep rich hue of this fine gem. Both the clarity and luster are exceptional- a rare feature for a stone this size. While faceted topaz of over 100 carats are not uncommon, a weight of over 500 carats is rare for the species and, combined with the qualities of exceptional transparency and luster, make this an excellent offering. Approx. 501 carats.