As already remarked, the refractive power of the Diamond is very high. The rays of light entering it are bent at a high angle, causing a large degree of what is called total reflection within the stone. The effect of this is to light the stone’s interior. Moreover, the rays of light are concentrated on a smaller part of the surface than is the case with less highly refracting minerals and thus also internal illumination is produced. The most important result of the high refractive power of the Diamond is the wide dispersion of the spectrum, causing the red rays to be widely separated from the blue rays and strong lights of one color to be transmitted to the eye as could not be the case were the different rays less widely separated. It is this power of flashing different colored lights which gives the Diamond one of its chief charms. The index of refraction ranges from 2.40 for the red rays to 2.46 for the violet rays. Ordinary glass has an index of refraction for the red rays of only 1.52 and for the violet 1.54, making the spectrum only about half as long as that produced by the Diamond.
Another pleasing property of the Diamond is the fact that it is usually more brilliant by artificial light than by natural, although some individual stones have a reverse behavior.
Diamond is much the hardest substance known in Nature, and as the proverb says only the Diamond is able to “cut Diamond.” It is ranked 10 in the scale of hardness on which minerals are classified, corundum being the next below it. It is really separated by a wide gap from the latter mineral, however, and its hardness is as much greater than that of corundum as that of corundum is greater than that of the first mineral in the scale. This hardness of Diamond affords a ready means of identifying it, as it will scratch all other substances. It is popularly supposed that Diamond is the only mineral which will scratch glass to any extent, and a stone found is often reported to be Diamond because it will do this. As a matter of fact, however, all quartz will scratch glass and the harder minerals, garnet, topaz, beryl and others will do so easily. Minerals which will scratch glass are therefore common. The Diamond cuts glass instead of scratching it, and is the only mineral that will do this. Although the Diamond is so hard, it is not tough, and can be easily broken with the blow of a hammer. It was a tradition of the ancients that if a Diamond were put upon an anvil and struck with a hammer, both hammer and anvil would be shattered without injuring the Diamond in the least. One occasionally hears this statement made even at the present day. It is entirely untrue, however, the Diamond being as brittle as at least the average of crystallized minerals. The specific gravity of the Diamond is about three and one-half times that of water, determinations showing variations between 3.49 and 3.53. Carbonado is lower, ranging between 3.14 and 3.41. Diamond is thus a comparatively heavy mineral, the only ones among the gems which much exceed it in specific weight being hyacinth, garnet, ruby, sapphire and chrysoberyl.
Diamond becomes strongly electric on friction so that it will pick up pieces of paper and other light substances. It does not retain its electricity long, however, usually not over half an hour. It is not a conductor of electricity, differing in this respect from graphite, which is a good conductor. Diamond becomes phosphorescent on rubbing with a cloth, giving out a light which is visible in the dark. Some stones emit such a light after being exposed to the sun’s rays for a time, as if they took it up from the sun and gave it out again. This has often been stated to be a property of all Diamond, but this is not true, only certain stones exhibiting it. As first suggested by Mr. Geo. F. Kunz, it is probable that this phosphorescence is due to minute quantities of hydrocarbons which emit light on being heated by the friction given the stone. It is curious to note that the light is in some cases given out only from certain crystal faces of the stone. Thus Diamonds are known which give out light from the cubic faces but not from the octahedral, while others are reported as giving out light of different colors from different faces.
The name Diamond comes from the Greek adamas, which means unconquerable. This term was doubtless applied because of the great resistant power assigned to it by the ancients. Besides the well known tradition that it could not be broken by hammer and anvil, they believed that it could be subdued or broken down only when dipped in warm goat’s blood. Our words adamant and adamantine are also derived from adamas, the latter term still being used to describe the luster of the Diamond. The change of adamas into the word Diamond is thought by some to have come from prefixing to it the Italian diafano, transparent, in allusion to its possessing this property.
According to classical mythology the Diamond was first formed by Jupiter, who turned into stone a man known as Diamond of Crete, for refusing to forget him after he had ordered all men to do so. Many medicinal virtues were ascribed to the Diamond, it being regarded as an antidote for poisons and a preventive of mania.
The world’s supply of Diamonds has come almost wholly from three countries—India, Brazil and South Africa. Up to the beginning of the eighteenth century India was the only source of Diamonds known. The Diamond fields of India occur chiefly in the eastern and southern portions of the peninsula. The famed region of Golconda is in the southern part. This is the territory whence have come the most celebrated Indian stones, such as the Kohinoor and the Hope Blue. The French traveler Tavernier reported when he was there in 1665, that sixty thousand men were then employed in these mines. Now the mines have all been given up and the region is abandoned.
The present yield of Indian Diamonds comes almost wholly from mines in a district south of Allahabad and Benares. The Diamonds occur here, as universally in India, in a conglomerate or sandstone made up of the remains of older rocks.
The mines are worked almost wholly by natives of the lower caste, attempts of Europeans to conduct the mining not having met with success. The natives separate the Diamonds by washing, or where the rock is too hard for such methods, break it up by heating and throwing cold water upon it. The production of Diamonds from all of India is at the present time very small, not reaching a million dollars a year in value. It is likely in time to disappear altogether since most of the old mines have been abandoned and even their location forgotten and the returns from the present mines are not very profitable.
The Brazilian Diamond fields were the first important ones to become known after those of India. Diamonds were first found here in 1729 in river sands which were being worked for gold by adventurers who penetrated into the region from the coast. The gold miners paid no attention to the bright crystals sometimes seen in the bottoms of their pans, but a monk who had seen Diamonds mined in India recognized them as gems indeed. While for many years the Diamonds obtained came wholly from the river sands, later, upland deposits were discovered which now afford a part of the supply. Diamonds have been found in the following provinces of Brazil: Bahia, Goyaz, Matto Grosso, Minas Geraes and Parana. In all except Bahia and Minas Geraes the mining is desultory and consists simply in washing river sands by means of wooden bowls. Enough Diamonds are thus obtained to afford a precarious living to the garimperos, as they are called, who follow this occupation. The chief Diamond bearing region of Brazil at the present time is in the province of Minas Geraes, centered about the city of Diamantina. The black variety of Diamond known as carbonado comes chiefly from the province of Bahia and is in large demand for industrial purposes. The Brazilian Diamonds are as a rule small, but exceed all others in luster. The largest Brazilian Diamond known is that named Star of the South, which weighed in the rough 254.5 carats and was valued at one hundred and seventy-five thousand dollars.