In mineralogy, diamond (from the ancient Greek adámas, meaning "proper" or "unalterable") is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is the second most stable form of carbon, after graphite; however, the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond is specifically renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material synthesized so far. Those properties determine the major industrial application of diamond in cutting and polishing tools.
Diamond has remarkable optical characteristics. Because of its extremely rigid lattice, it can be contaminated by only few types of impurities, such as boron and nitrogen. Combined with the wide transparency, this results in clear, colorless appearance of most natural diamonds. Small amounts of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green, purple, pink, orange or red. Diamond also has relatively high optical dispersion, that is ability to disperse light of different colors, which results in its characteristic luster. Excellent optical and mechanical properties, combined with efficient marketing, make diamond the most popular gemstone.
Sunday, August 16, 2009
Gemstones and their distribution
A large trade in gem-grade diamonds exists. Unlike other commodities, such as most precious metals, there is a substantial mark-up in the retail sale of gem diamonds. There is a well-established market for resale of polished diamonds (e.g. pawnbroking, auctions, second-hand jewelry stores, diamantaires, bourses, etc.). One hallmark of the trade in gem-quality diamonds is its remarkable concentration: wholesale trade and diamond cutting is limited to just a few locations; 92% of diamond pieces cut in 2003 were in Surat, Gujarat, India. Other important centers of diamond cutting and trading are Antwerp, where the International Gemological Institute is based, London, New York City, Tel Aviv, and Amsterdam. A single company—De Beers—controls a significant proportion of the trade in diamonds.They are based in Johannesburg, South Africa and London, England. One contributory factor is the geological nature of diamond deposits: several large primary kimberlite-pipe mines each account for significant portions of market share (such as the Jwaneng mine in Botswana, which is a single large pit operated by De Beers that can produce between 12.5 to 15 million carats of diamonds per year), whereas secondary alluvial diamond deposits tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometers (e.g., alluvial deposits in Brazil).
Synthetics
Synthetic diamonds are diamond crystals that are manufactured in a laboratory, as opposed to natural diamonds which form naturally within the Earth. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.
The majority of commercially available synthetic diamonds are yellow in color and produced by so called High Pressure High Temperature (HPHT) processes. The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of boron or from irradiation after synthesis.Colorless gem cut from diamond grown by chemical vapor deposition
Another popular method of growing synthetic diamond is chemical vapor deposition (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically 1 to 99 methane to hydrogen) into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch or laser.This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).
At present, the annual production of gem quality synthetic diamonds is only a few thousand carats, whereas the total production of natural diamonds is around 120 million carats. Despite this fact, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are fancy-colored.
The majority of commercially available synthetic diamonds are yellow in color and produced by so called High Pressure High Temperature (HPHT) processes. The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of boron or from irradiation after synthesis.Colorless gem cut from diamond grown by chemical vapor deposition
Another popular method of growing synthetic diamond is chemical vapor deposition (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically 1 to 99 methane to hydrogen) into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch or laser.This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).
At present, the annual production of gem quality synthetic diamonds is only a few thousand carats, whereas the total production of natural diamonds is around 120 million carats. Despite this fact, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are fancy-colored.
Simulants
A diamond simulant is defined as a non-diamond material that is used to simulate the appearance of a diamond. Diamond-simulant gems are often referred to as diamante. The most familiar diamond simulant to most consumers is cubic zirconia. The popular gemstone moissanite (silicon carbide) is often treated as a diamond simulant, although it is a gemstone in its own right. While moissanite does look similar to diamond, its main disadvantage as a diamond simulant is that cubic zirconia is far cheaper and arguably equally convincing. Both cubic zirconia and moissanite are produced synthetically.
Brilliance, Polish and Symmetry of a Diamond
Cut of a diamond affects its Brilliance (reflection of light), whereas Polish (smoothness of facets) and Symmetry (alignment of facets) affect the sparkle of a diamond. A poor polish can make a diamond look dull and a poor symmetry can misdirect the light reducing the sparkle. Types of Cut There are three types of cuts as shown in the figure: Shallow CutIn which light refracts away through the bottom. Ideal CutIn which light gets reflected through the top producing maximum brilliance. Deep CutIn which light refracts away through the sides.
GIA Cut Grading Diamond cuts are graded on the following scale established by the Gemological Institute of America (GIA): Excellent Cut:The rarest cut grade of all, Excellent cut reflects maximum light entering the diamond and thus shines with optimum brilliance. Very Good Cut: Very Good cut grade may cost less than the Excellent cut, but it is equally beautiful and brilliant. Good Cut: Good cut grade of a diamond helps reflect light to obtain a good amount of brilliance, though not equal to the Excellent or Very Good cut. Thus it demands a much lesser price. Fair Cut: Being not as brilliant as a Good cut, Fair cut grade quality diamonds refract less amount of light, but make a better choice than Poor cut diamonds. Diamond Dimensions The various dimensions of a diamond are defined as follows: Table: The topmost and largest facet of a diamond. Crown: The sloping section of a diamond- from the girdle to the table. Girdle: The point where the crown and pavilion meet, which also determines the perimeter of the diamond. Diameter: The width of the diamond measured with reference to the girdle. Pavilion: The lower section of a diamond from the girdle to the culet. Culet: The tip of a diamond (the best culet is invisible to the naked eye). Depth: The height of a diamond measured from the culet to the table
GIA Cut Grading Diamond cuts are graded on the following scale established by the Gemological Institute of America (GIA): Excellent Cut:The rarest cut grade of all, Excellent cut reflects maximum light entering the diamond and thus shines with optimum brilliance. Very Good Cut: Very Good cut grade may cost less than the Excellent cut, but it is equally beautiful and brilliant. Good Cut: Good cut grade of a diamond helps reflect light to obtain a good amount of brilliance, though not equal to the Excellent or Very Good cut. Thus it demands a much lesser price. Fair Cut: Being not as brilliant as a Good cut, Fair cut grade quality diamonds refract less amount of light, but make a better choice than Poor cut diamonds. Diamond Dimensions The various dimensions of a diamond are defined as follows: Table: The topmost and largest facet of a diamond. Crown: The sloping section of a diamond- from the girdle to the table. Girdle: The point where the crown and pavilion meet, which also determines the perimeter of the diamond. Diameter: The width of the diamond measured with reference to the girdle. Pavilion: The lower section of a diamond from the girdle to the culet. Culet: The tip of a diamond (the best culet is invisible to the naked eye). Depth: The height of a diamond measured from the culet to the table
ABOUT DIAMONDS
A diamond is lot more than just a precious stone. It is the testimony of a joyous occasion and a souvenir full of emotions. At B2C Jewels we understand this very well and bring you a guide to enrich your diamond knowledge, so you can buy diamonds confidently and make a better and easier purchase.
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