This group includes all those stones that have been traditionally represented in the trade. The name diamond refers to its hardness (Greek- Adamas, the unconquerable). There is nothing comparable to it in hardness. its cutting resistance is 140 times greater than that of ruby and sapphire, the gemstone next in hardness after diamond. However the hardness of a diamond is different in the individual crystal directions. This allows one to cut diamond with diamond and diamond powder. Because of the perfect cleavage, care must be taken not to accidently bang againts an edge of a diamond and also when setting it. Its very strong luster sometimes enables the experienced eye to differentiate between a diamond and its imitations.
Diamond is generally insensitive to chemical reactions. High tempertures, on the hand, can induce etchings on the facets. Therefore special care must be taken during soldering!
Diamonds are found in primary and secondary deposits. Until 1871 diamonds were only washed out of diamondiferous placers. By chance a primary deposit was discovered in South Africa: volcanic pipes filled with diamond-bearing rock, kimberlite (more rarely lamproite, a greenish-gray speckled mafic rock).
Diamond is formed at great depth (as much as 150-300 km) at very high temperatures and high pressures. By particular kind of volcanic eruption, they came to the surface of the earth or close to it with rising magma. With gradual erosion, the original volcanic cone was removed, exposing the kimberlite pipes.
Up to the 18th century, some diamonds came from Borneo, but most from India. In 1725 the first diamonds were found in the South American continent in Minas Gerais in Brazil. In 1843 a brown-black carbonado was discovered in Bahia; this is a microcrystalline aggregate that is very tough and therefore in demand for industry.
Brazil was superseded by South Africa, which until about 1970 had an unsurpassed position as to production and trade. The first diamond find in 1866 was in the region near the source of the Orange River. At first only the alluvial deposits were worked. In the meantime many kimberlite pipes have been discovered.
The most famous and noteworthy pipe of South Africa, the Kimberley mine, was worked from 1871 to 1908 without any machinery. This produced what was once the largest man-made hole, the so-called Big Hole: the surface hole has a diameter of 1510ft (460 m), and the depth is 3510 ft (1070 m). Today it is half-filled with water. Altogether 14.5 million carats (2900 kg or about three tons) of diamonds were found there. after having been worked for a short time underground, the mine was discontinued in 1914, because it proved not economically feasible. Other South Africfan pipe mines changed from open pit to underground mining early on. Ashaft is sunk next to the kimberlite pipe, and then the diamond-bearing rock is mined along transverse levels.There are important alluvial deposits in Namibia at the western edgeof the desert Namib.
In the valuation of faceted diamonds, color, clarity, cut and carat are taken into consideration. These four c's decide that value of a diamond;
The color evaluation of most gem_quality diamonds is based on the absence of color.
A chemically pure and structurally perfect diamond has no hue, and consequently, a higher value.The GIA Color Grading System measures the degree of colorlessness by comparing a stone, under controlled lighting and precise viewing conditions, to masterstones of established color value. Many of these color distinctions are so subtle that they are invisible to the untrained eye; however, these distinctions make a very big difference in diamond quality and specialy price.
Natural diamonds are the result of carbon exposed to tremendous heat and pressure deep in the earth. Evaluating diamond clarity involves determining the number, size,nature, position and color of these characteristics, as well as how these affect the overall appearance of the stone. While no diamond is perfectly pure, the closer with comes, the higher its value.
Many inclusions and blemishes are too tiny to be seen by anyone other than a trained diamond grader. To the naked eye, a VS1 and an SI2 diamond may look exactly the same, but these diamonds are quite different in terms of overall quality.
Diamonds are beautiful for their ability to transmit light and sparkle so intensely.
The quality of cut is crucial to the diamond's final beauty and value. Brightness, Fire and Scintillation, consider the diamonds overall face-up appearance.
Brightness: Internal and external white light reflected from a diamond.
Fire: The scattering of white light into all the colors of the rainbow.
Scintillation: The sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the diamond.
The measurement of how much a diamond weighs.
A metric " carat " is defined as 200 milligrams. Each carat can be subdivided into 100 points. The weight of a diamond below one caret can also be described by its points alone.
Diamond price increases with carat weight, beacuse larger diamonds are more rare and more desirable. But two diamonds of equal carat weight can have very different values depending on three other factors within the 4C's: clarity, color and cut.
The winning of diamonds from the host rock is done today with a great deal of machinery. The least expensive method is to loosen the diamonds from placers and weathered kimberlite, the yellow ground. Because of the loose texture, the diamonds, due to their high density, can be separated and accumulated in pans. The blue ground, the pipe matrix, must first be cut into small pieces with stone crushers, before it can be washed in the same way. The separation of the diamonds from the concentrate, originally exclusively done by hand, is done today almost fully automatically. The tendency of diamonds to adhere to grease is also utilized. Diamond is, in contrast to other materials, hard to moisten, i.e., even in water it actually does not get wet. Therefore, from the concentrate, wich glides over grease vibrating tables, the diamonds get suck to the grease, while other minerals continue to glide along.
A number of diamonds are well known and famous because of their size, beauty m or their adventurous past.
1. Cullinan 530.20 carats. Cut from the largest rough gem diamond ever found of 3106 carats, the Cullinan (named after Sir Thomas Cullinan, chairman of mining company) together whit 104 other stones, by the firm Asscher in Amsterdam in 1908. Adorns the sceptre of the English king's insignia . Kept in the Tower of London; largest cut diamond of fine quality.
2. Dresden Green, 41 carats. probably from India; early history not known. Supposedly bought in 1742 by Friedrich August II, Duke ofsaxony, for 400,000 taler. kept in the Green Vaults in Dresden, Germany.
3. Hope 45.52 carats.Appeared 1830 in the trade and was bought by the banker H.ph.Hope (hence the name). Probably recut from a stolen stone.Since 1958 in the Smithsonian Institution, Washington , D.C.
4. Koh-i-Noor 108.92 carats. Originally a round stone of 186 carats belonging to the Indian Raj.Plundered in 1739 by the shah of persia, who called it "Mountain of Light" (Koh-i-Noor). Came into possession of the English East India Company, which presented it to Queen Victoria in 1850.Recut, it was set in the crown of Queen Mary , wife of George V, and then in a crown made for the mother of Queen Elizabeth II; now in the Tower of Landon.
5.shah 88.70 carats. Came frome India , shows cleavage planes, partially polished.Has three inscriptions of monarchs' names (amongst them the Shah of Persia's- hence the name ). Given in 1829 to Tsar Nicholas I. Kept in the Kremlin, Moscow.
6. Florentine 137.27 carats. Earlyhistory steeped in legend. In 1657 in the possession of the Medici family in Florence (hence the name). During the 18th century in the Habsburg crown, then used as brooch.Whereabouts after World War I are unkhown.
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