Diamond! The word spells magic and fantasy to every one. They are nothing but highly prized gemstone endowed with mesmerising brilliance, beauty and magnificence. From time immemorial diamonds have been the most cherished and sought after possessions of mankind not only for the fascination they hold but also their high intrinsic value, ornamental utility and astrological beliefs. Diamond is an ultra hard cubic form of carbon and is the hardest known substance, a strategic mineral critical to the market in super abrasives. The diamond, unbelievably, has the simplest chemical composition consisting of a single element namely, carbon with traces of nitrogen, boron, etc. Interestingly, the chemical composition of diamond is the same as that of graphite - which is used in the making of pencils, crucibles and also as lubricant. But diamond is the hardest mineral on the earth and graphite is one of the softest.
Loose heart shaped diamonds
Loose heart shaped diamonds
CARBON: THE SOURCE OF FORMATION OF DIAMOND
Carbon constitutes only around 1% of the weight of the earth’s crust. Earth cannot be imagined without carbon. Living substances including human beings, animals and vegetation can not survive with out the presence of carbon. Marbles, which decorate our houses; limestones, the basis for cement industry; and coal or oil, the energy minerals, would not have formed without the simple element carbon. Apart from its presence in living substances and occurrence in soils, peat, coal, sedimentary rocks, etc., carbon is also found in the atmosphere and oceans. Without carbon dioxide the climate of the earth would have been much colder. The chief element in diamond too is none other than the carbon often containing up to 99.9%.
DIAMOND: THE KING OF GEMSTONES
Diamonds have long been prized as precious stones because of their beauty, rarity, and permanence. Among the gemstones, diamond reigns supreme and is referred to as King Gem as it is endowed with some unique properties like extreme hardness, beauty, supreme brilliance, rarity, durability, which makes it very attractive. Because of its extreme hardness - diamond only cuts diamond. A carat is the unit of weight for diamonds, a carat weighs 200 mg..
Natural diamonds are probably the oldest and are messengers from deep interior of earth. The growth morphology of natural diamond is often octahedral but dodecahedral crystals are also common. In its natural state, diamond occurs as rounded, rough-looking pebbles, appearing similar to pieces of gum arabic. Diamond is a beautiful substance in many ways. It’s simple but elegant crystal structure, in which each carbon atom is bonded to four other atoms in a tetrahedral arrangement, yields a strong rigid framework.Many may not believe that such simple carbon, which is the basis of all life on the earth, gives rise to form most beautiful Diamonds.
Diamond crystals recovered from Timmasamudram Kimberlite, Anantapur district, Andhra Pradesh
Diamond crystals recovered from Banaganapalle conglomerate, Kurnool district, Andhra Pradesh
DIAMONDS FROM 150 KM DEPTH!
Scientists have proved that diamonds can form and grow in molten magma when pressures reach hundreds of tonnes per square inch in the range of 45 to 60 thousand atmospheres or kilo-bars in the company of equally high temperatures in the range of 900o to 1300o C. Such pressure-temperature regimes prevail only in the deep interiors (150 to 200 km or more depth) of the earth below the Cratonic areas, which are nothing but stable and ancient parts of the earth’s crust. Most of the pressures we experience at surface in our day-to-day life are rather very modest and do not even exceed more than a few tens of atmospheres. The zone or area of diamond formation in the upper mantle (below 150 to 200 km or more) is generally referred to as diamond stability field or diamond window. The magmas generated around this zone are called kimberlite and Lamproite .They are small volume volcanic rocks brought to the surface of the earth in a violent eruption event. During their quick ascent to surface they pick up chunks of diamondiferous rocks, such as peridotite and eclogite, the parent rocks in which diamonds are formed. The kimberlites and lamproites in fact, act as transporting agents of diamonds, formed at depth, to the surface of the Earth. The travel time of kimberlite/lamproite magmas is less than five hours, it attains super sonic speed as it nears the surface of the earth, lest the diamonds being transported will burn out or get converted to graphite. But for the kimberlites and lamproites we would not have seen diamonds! Scientists have estimated that the oldest kimberlites emplaced into earth crust were around 1800 million years ago whereas the oldest diamonds were formed around 3300 million years ago. Recent research suggests that some rare diamonds are derived from even greater depths-the deep upper mantle, the transition zone (410-660 km), and the lower mantle
Vertical section through Earth’s crust - mantle. The uppermost, non-convecting portion of Earth including the crust and part of the upper mantle is called the lithosphere, and the underlying convecting part the asthenosphere. Beneath ancient cratons the lithosphere may extend to about 200 km depth. In cooler regions of Earth’s mantle the graphite/diamond transition occurs at shallower depth. Beneath cratons, therefore, there is a region where lithosphere and diamond stability overlap and this is the main source region of diamonds worldwide (after Mitchell, 1994)
Diamondiferous upper mantle rocks, such as peridotite and eclogite, the parent rocks in which diamonds are formed, which are transported to the surface by kimberlites/ lamproites.
HISTORICAL ACCOUNTS OF DIAMOND MINING IN INDIA
The world was introduced to the splendour and glory of these rarest of rare gems by our great country. Diamonds are known in India for more than 2500 to 3000 years, figured in the Indian epic Mahabharata and Hindu Puranas and in the writings of Kautilya (4th century B.C), Pliny (1st century A.D.), Ptolemy (2nd century A.D.), Varahamihira (6th century A.D.) and others. In the ancient Deccan, according to the Kautilya’s Arthasastra (Kangle, 1972), diamonds were reported from Sabharastra (Vidarbha in Maharashtra) and according to Varahamihira’s Brhat Samhita, from the Vena River (modern Wainaganga, Maharashtra) and Matanga country, identified as the area covering a part of the erstwhile Hyderabad State, which included the Krishna and Godavari districts. There is no well-documented record of the diamond mining during the ancient period, but the accounts of the medieval period (13th - 18th centuries A.D.) by European travellers and merchants, and Portuguese and British officials gave vivid descriptions of the hectic diamond mining activity of those days. Prominent among them were Marco Polo (13th century), Nicolo de Conti and Asthanasius Nikitin (15th century), Fernao Nuniz and Garcia da Orata (16th century), Jacques de Coutre, Jean Baptiste Tavernier and Henry Howard (17th century), Benjamin Heyne, Henry Voysey, and Capt. New Bold (19thcentury) and officers of the Geological Survey of India during the 19th & 20th centuries viz., William King, Bruce Foote, Valentine Ball, Heron and others described the diamond fields and mining activity. The writings of Tavernier (1676) in the "Travels in India" and the Paper presented by Henry Howard (1677), the Right Honourable the Earl Marshall of England, to the Royal Society, gave us details of the 17th century account of the different mines worked, nature of material mined, methods of working, cutting, trading of diamonds etc.
Generalised location map of ancient and modern diamond occurrences in India
THE PAST GLORY OF GOLCONDA
Golconda (Golkonda), known as Mankal or Mangalawaram in medieval times, was originally fortress of the Kakatiya rulers (11th to 14th centuries A.D.) before Sultan Quli Qutb Mulk, the founder of the Qutb Shahi dynasty made it capital of his government, under the Bahmani rulers of the Deccan, in A.D. 1497 and renamed it Muhammadnagar in honour of the Bahmani king, Muhammad. Located on the main trade route between Surat (Gujarat) and Masulipatnam (Andhra Pradesh), the Golconda town developed into a trading mart for several commodities including the Deccan diamonds. The Golconda town is on the outskirts of the modern Hyderabad. Karwan (Carvan), located about 5 km to the east of the Golconda fort, became a thriving cutting and trading centre for diamonds during the reign of Ibrahim Qutb Shah (A.D. 1550-80).
Thus Golconda became famous the world over, as the Diamond Capital in the past. The mining activity declined by about the beginning of the 18th century A.D. most probably due to exhaustion of the main deposits, non-patronage of the waning kingdoms and discovery of new diamond fields in 1725 in Brazil.
Golconda - Diamond Capital of the Medieval Period.
ANCIENT MINES AND THE WORLD FAMOUS DIAMONDS
There were several diamond mines in the past, all located in the modern Andhra Pradesh (A.P.) with the exception of those at Raichur in Karnataka and Wairagarh in Maharashtra .The diamond fields in A.P., spread over an area of 50,000 sq km were confined to the drainage basins of the Krishna and Pennar Rivers
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