Black diamonds, low grade, flawed stones, ‘bortt’ and ‘Carbonade’, are of industrial value and used extensively for polishing the surface of metals, minerals, etc. and in gem-cutting.
Production and Distribution:
Diamond deposits occurring three types of geological settings such as kimberlite pips, conglomerate beds and alluvial gravels. The main diamond bearing areas in India are Panna belt in Madhya Pradesh, Munimadugu-Banganapalle conglomerate in Kurnool district, Wajrakarur kimberlite pipe in Anantapur district and the gravels of Krishna river basin in Andhra Pradesh. Reserves have been estimated only in Panna belt and Krishna Gravels in Andhra Pradesh.
The total in situ reserves are about 26, 43,824 carats. There are conditional resources of 19, 36,512 carat. Thenew kimberlite fields are discovered recently in Raichur-Gulbarga districts of Karnataka. The main diamond bearing areas in India are Panna belt in Madhya Pradesh, Mummadugu-Banganapalle conglomerate in Kurnool district, Wajrakarur Kemberlite pipe in Anantapur district and the gravels of Krishna river basin in Andhra Pradesh, Panna diamond belt is the most important area.
This belt spreads over the districts of Panna, Chhatarpur and some parts of Satna. Reserves have been estimated only in Panna belt and Krishan gravels. In addition to the recoverable reserves of about 0.982 million carats, there are conditional resources of 1896 thousand carats. The production of diamond was 34580 carat in 1998 which increased to 9167.12 carats in 2003-2004.
De Beers was granted permission by the State Government of Orissa to conduct an aerial survey over 10,000 kms of diamond deposits in the state. The state government would provide only a prospecting license if the company set up a diamond processing plant in the state. Diamond bearing volcanic pipes and Kimberlite Carbonatite dykes has been discovered in the Krishna valley and Panna diamond field areas of Madhya Pradesh.
The principal diamond-ferrous stratum is thin layer of conglomerate locally known as ‘Mudda’ in the matrix of which diamonds occur. The cutting and polishing activity is concentrated in and around Surat, Navasari and Ahmedabad in Gujarat. Other traditional centres for diamond cutting are Palanpur, Bhavnagar and Bombay. Cambay, Jaipur, Trichur and Goa are comparatively new centres. Industrial diamonds are generally consumed in the manufacture of drill bits, grinding tools and stone cutting and polishing machines.