Brazil

Curiously enough, just as the Indian Diamond mines began to fail a new source appeared, for in 1725 Diamonds were discovered in Brazil in the state of Minas Gerais, and then later at Bahia. This had a tremendous impact on the world Diamond market. By 1727 a collapse of world market prices of Diamond had set in. So fearful were dealers of the effect of Brazilian Diamonds that they spread the false report that any Brazil Diamonds which they handled came from India, having, they said, been sent to Brazil first. The Portuguese Government imposed a monopoly on Diamond mining, the restriction being removed only in 1822 when Brazil achieved political independence.

The year 1842 saw the discovery in Bahia of the important variety of Diamond called carbonado and from here, the only source, it is still mined. Carbonado is not truly single crystal of Diamond but is a (black) conglomerate of Diamond crystals locked together in a maze of different orientations. This makes it of very great value for technological uses. The great weakness of Diamond as a tool is the ease with which it can cleave when misused. Now, carbonado cannot cleave, for if one of the interlocked small crystals is in fact induced to cleave, the cleavage merely runs along the short length of this crystal and is then locked in by a misoriented neighbor. Conse­quently, carbonado is extremely strong. At first this was not really fully realized and 'Brazilian Carbons', as they were called, were not regarded as of any especial value. Yet this 'cryptocrystalline' character makes the carbonado of great service as a drilling tool and for shaping hard materials.

It is of particular note to draw attention to the great change which took place in the price of carbonado when its industrial potentialities became recognised. Discovered in 1842, seven years later in 1849 the price of this material (treated as rubbish) was sevenpence per Carat. Thirty years later the price had shot up to 20 shillings a Carat. Twenty shillings in 1879 could probably buy at least what £10 can buy today, if not more. It became common practice to use pieces of carbon­ado of from 3 to 5 carats or so, and such pieces would fetch £10 (in 1879!).

The Diamond deposits in Brazil occur both in low-lying river valleys and on high plateaux, but so far the original pipes have not been found. Most Brazilian Diamonds are small, the valuable carbonado being picked out by hand. The largest piece of Diamond material ever found in the world is a single piece of carbonado unearthed some 60-odd years ago and weighing 3148 carats. It was sold for over £3600. Several large fine-quality Brazilian gemstones have also been found. One of these weighed 262 carats, was sold for £40 000, and was cut into a 129-Carat gem named Star of the South. Largest of all the Brazilian Diamonds is the 'President Vargas', found in 1938 and weighing 726 carats.

Brazil is today one of the smaller of the world producers, with an annual output of the order of 350 000 carats. Some of the carbonado is mined from river-beds by divers.

India and Brazil (and to a slight extent Borneo) were the principal sources till 1851, when small Diamond finds were reported in New South Wales. Although a succession of Australian findings has been made, the total Australian output is not of much significance in terms of world consumption now.