gemstones or gem materials are stones or materials from which a gem may be cut. By popular perception, a gem is a rarely encountered hard, durable, brilliantly shining and beautiful natural mineral which has high intrinsic value. Three characteristics of a gem stand out persistently. These are: rarity, durability and beauty. Rarity is an economic function of supply and durability is a measurable physical attribute, but beauty is person-specific carrying different meanings to different individuals, and may include properties like colour, ability to take polish, sheen, size, shape, etc.
(1) Rarity: The mode of transportation of diamonds for long distances up the difficult paths make them scarce, and of the diamonds, the gem types are scarcer as their lower share in the total production indicates. By the law of demand-supply, the scarcer a commodity is, the higher its value. This is one of the important reasons why high values are attached to gem diamonds.
(2) Durability:A diamond is the hardest natural substance having a hardness of 10 in the Mohs scale. Besides, it is not affected by acids. The hardness and acid-resistance make it durable. The mode of its formation under extremely stressful conditions of heat and forces over long durations of time down in the earth’s mantle and crust has contributed to this hardness. Its only weakness is that it is vulnerable to breaking with a sharp accurate blow due to its cleavage. But on its own it is indestructible. (3) Colour: As has been mentioned, diamond contains 98.9% C12 and 1.1% C13 which
may be partially replaced by some foreign elements. When the C13 is evenly
dispersed without any foreign element, then the diamond is absolutely colourless (also referred to as ‘white diamond’). The mystery of coloured diamonds was solved by researchers of the Bell Laboratory, USA in 1957, when they heated a diamond specimen to 20000C and detected the presence of nitrogen. Colours in diamond are produced due to deformity or inclusions of some foreign elements which in their turn introduce some distortions due to their differential atomic sizes vis-a-vis carbon. The commonest foreign element is nitrogen (type I) while boron (type IIb) is an extremely rare foreign element, and graphite is another. For every million carbon atoms, 1,000 may be replaced by nitrogen atoms which occur in the form of aggregates of 4-10 atoms and which are believed to have entered the diamond crystals due to prolonged exposure to high temperature and pressure during and after their formation. The nitrogen inclusion renders yellow colour to diamonds. The amount of boron when present, on the other hand, is miniscule – only one or two for every million carbon atoms. Boron causes absorption of the longer infrared rays of light and the diamond is seen as blue to bluish gray in colour. According to a report of research in the Florida University, USA and of Case Western Reserve University, Australia, the black diamonds owe their black colour to inclusion of nitrogen and
Diamond 131 hydrogen of extra-terrestrial origin. The other colours, namely, green, red, violet, gray, brown, etc. are due to deformities of the crystal structure (e.g., displacement of some carbon atoms) caused by natural radiation in the earth (e.g., electrons, neutrons, alpha particles, gamma rays) or by nitrogen. In nature, white, green and blue diamonds are very rare and hence highly valuable. Red diamond is the rarest.
(4) Clarity: Small bubbles and cracks that are called ‘feathers’ by jewellers, reduce the clarity of a diamond, and consequently, its value. But inclusions, which also affect the clarity, do not always reduce the value of a diamond, because diamonds owe their fancy colours due to them.
(5) Optical properties: Both refractive index and dispersion are high. Refractive index is 2.42 (cf. 1.53 for ordinary glass). Dispersion is the rate of change of refractive index with change in wavelength of the incident light, and it is mainly the combination of high refractive index and high dispersive power that renders brilliance to diamonds. Type-IIa diamonds transmit both infrared and ultraviolet light (in contrast to the Type-I diamonds which absorb them).
(6) Thermal properties: The Type-II diamond possesses the highest thermal conductivity (5 times that of copper). The extremely rare Type-IIb diamonds are extraordinarily heat-sensitive capable of registering as small as 0.0020C change in temperature. (7) Electrical properties: Although diamonds are electrically insulating materials, the
type-IIb diamonds behave as semiconductors. Semiconductors are materials with resistivity intermediate between metals (resistivity < 104
ohms/cm) and insulators (resistivity >103
ohms/cm).They contain only a small number of loosely bonded electrons at room temperature, and hence their conductivity is very poor (of the order of 100,000 times less than that of conductor metals). However, their low electrical conductivity can be substantially improved by addition of minute quantities of some foreign atoms of a different valency, one of which is boron (the process is called ‘doping’). The semiconductivity of the type II-b diamonds is on account of inclusion of boron atoms in them. Another characteristic of semiconductors in general is that their electrical properties can be controlled by supplying some external energy (e.g., optical energy, thermal energy). The electrical conductivity of type-IIb diamonds are extremely sensitive to changes in temperature as small as 0.0020C.
(8) Cut: Natural diamonds are somewhat dull to look at. It is only when they are cut into well defined faces and the faces are polished that diamonds show their characteristic brilliance. Diamonds being the hardest substance, can only be cut by another diamond (nowadays by laser also) and can only be polished by diamond dust. The cutting requires a very high degree of skill – particularly when the individual pieces are as small as 1/250 carat or less than a milligram in weight (the size for which Indian cutting and polishing industry is famous), and that too when a large number of faces are to be developed (the highest valued ‘brilliant cut’ consists of 58 faces). More the number of faces, more will be the brilliance of the diamond.
(9) Specific gravity: Diamond is moderately heavy, its specific gravity being 3.53. The value/volume ratio is very high for diamond.
(10) Caratage: Gem diamonds, and for that matter, any gem, are bought and used as individual pieces. So the individual weights of the pieces are important for
determining their values. Moreover, the larger a diamond is, the rarer and, hence, more valuable it is. Occurrence of such diamonds is not predictable and are encountered by chance in course of mining and to give each of them a unique identity, a fancy name is given to it. Some large diamonds thus found during the nearly three millennia of history of diamond mining, have carved permanent niches in legends and literature. Initial caratage of a rough is all the more important because up to 40-50% of it may be lost during cutting and polishing in order to convert it to a gem. A few examples of famous large roughs are: Culliman (3,106 carats, found in 1905 in Premier mine of South Africa), Excelsor (995.2 carats, found in South Africa in 1893), Great Moghul (817 carats, found inKollur mine, Golkonda, India in the 17th century), Jonker ( 726 carats, discovered in 1934), Orloff (Russia), Koh-i-noor (original weight believed to be 800 carats and believed to be found in Golkunda, India, first recorded in 1304), Regent (India), Blue Hope (115 carats, found in India in 1668). These sizes may be compared with those generally produced from Majhgaon mine in India (0.01-0.70 carats), and the fact that hardly 400,000 pieces of the diamonds produced in the world are of more than 2 carats in size. In the recent past, notable large pieces produced from Majhgaon mine are one weighing 30.33 carats (valued Rs 9.2 million) in 2003 and another weighing 27 carats (valued Rs 9.6 million) in 2005.
(11) Certification: For a common retail buyer, the physical and optical properties of diamonds carry little sense, and he is most concerned, besides size, with the colour and brilliance as judged with the naked eye. But both these characteristics can be replicated by unscrupulous people. So for him certification by some trusted authority or agency assumes importance.
(12) Aggressive marketing: Almost any gemstone can be sold irrespective of colour and cost, provided the basic criterion of rarity is met. Economically, demand of diamonds (for that matter any gem) is by and large elastic, i.e., they are luxury items, and not essential in our lives. Consequently, gems do not follow the conventional law of demand and supply according to which, demand generates first and supply follows. On the other hand, in case of gems, supply comes first and demand generates later in response to that. A classic example is provided by what is called Champagne diamond. When Rio Tinto first came out with yellowish brown diamond from its Argyle mine, it could not find takers as it looked cheap and ordinary. Then the company got it cut into small sizes in India with cheap skilled labour, and gave it the fancy name ‘Champagne diamond’. It immediately caught the attention of designers to use them as sequins on garments. At the 2004 Oscar ceremony in Los Angeles, one actress wore a dress studded with 2,000 Champagne diamonds totaling 3,000 carats and valued at $2.5 million. It became a craze overnight – particularly a preferred choice for people with darker complexion.
(13) Therapeutic value: Diamond is traditionally believed to possess many direct therapeutic values for the internal functions of human body as well as for skin. Besides, it is believed by many to have some indirect beneficial effect on body and mind if worn on the body. This branch of therapy known as gemmotherapy works on the hypothesis that different gems, when worn by a man on his body, react differently to different kinds of cosmic rays having different effects on the health of his mind and body. It is a scientific fact that mesons produce cosmic rays which come from
Diamond 133 outside the earth in varied intensities every minute, and day and night about 600 rays pass through our body. Gemmotherapists believe that each kind of cosmic ray has some specific effect on human health, and each gem modifies these effects by preferentially absorbing or transmitting specific rays.
(14) Beliefs and superstitions: Diamonds (for that matter, gems at large), many people believe, bring luck or misery to lives.
(15) Stability of value: Economic phenomena like inflation, stagflation, recession and even political instability which exercise adverse impact on other manufacturing and processing sectors, do not affect adversely the demand of diamonds.
B. Industrial diamond: So far as industrial diamonds are concerned, most of the criteria