Just like a blood type for humans, diamonds have 4 distinct groups based on their crystalline structure. Type 2a and Type 2b stones are the most rare and usually sought after by connoisseurs and collectors.
Type 1a diamonds contain clusters of Nitrogen atoms throughout the crystal structure. Those stone usually display some degree of yellow color. Really nothing to write home about.
Type 1b diamonds contain singular Nitrogen atoms. These stones are 0.1% of all diamonds with strong orange, brown and sometimes green color.
Type 2a diamonds lack Nitrogen in their crystal structure. They represent no more than 2% of all natural diamonds and are the most valuable. Fancy colored type 2a diamonds could be pink or purple. Colorless 2a stones are exceptionally white and are typically traced to the Golconda mine in India.
Type 2b diamonds contain traces of Boron within the crystal. They are those blue or blue/gray diamonds everyone is craving to collect. They represent only 0.1% of diamonds.
2,000 years before diamonds were discovered in Brazil and South Africa, the only source of diamonds in the world came from the Indian mines of Golconda. These famous mines are located near present-day Hyderabad and were named for the 14th-century India sultanate.
The “Golconda” designation suggests that the stone's origin can be traced all the way back to the historic mine. By the beginning of 18th century the mine had exhausted its supply of raw gems.
A disproportionate number of the world's most famous diamonds came from Golconda, some of them are: