Emerald and diamond ring, circa 1890. Colombian emeralds are widely held to be the best in the world, and have been the world's primary source of quality emeralds for centuries. Colombian emerald deposits are special because geologically they are formed differently from those elsewhere, being the result of hydrothermal deposits. The result is a stone of unrivalled colour, as demonstrated by the central stone in this ring, in its original antique octagonal 'emerald' cut. This traditional three-stone ring is mounted in warm yellow gold, and its central emerald is flanked by a pair of well-matched antique old European-cut diamonds, the gaps between the stones ingeniously filled with rose-cut diamonds, adding an extra element of life and sparkle to an already classically beautiful antique 19th century ring.