Golconda Type IIa diamond ring. Centrally set with a cushion shape old mine Golconda Type IIa diamond, E colour, SI1 clarity with a weight of 3.58 carats in an open backclaw setting, flanked by eight round old cutdiamonds in open back grain settings with a combined weight of 0.08 carats. The total approximate diamond weight is 3.66 carats, to an impressive solitaire design with curving claws, linear open gallery and intricately pierced backholing, flanked to either side with raised open shoulders which terminate to fine ribbed details before flowing to a solid D-shapeshank. Testedplatinum, circa 1905, accompanied by Gemological Institute of America report #2141498398.
Diamonds are classified by scientists into two main types, depending on the presence of nitrogen in the diamond's chemical makeup. Type II diamonds contain little to no such impurities. This type is further subdivided into two groups, ‘a’ and ‘b’, both of which make up less than two percent of all gem quality diamonds. Type IIa diamonds are extremely rare, and the most pure of all diamonds, and consequently exhibit superior transparency. This type was first identified as coming out of India, namely the Golconda region. Some of the most famous diamonds in the world are Type IIa, including the Koh-i-noor and the Cullinan I.