Bbc africa business report botswana agate

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Bbc africa business report botswana agate

Diamonds have been known in India for at least 3, years but most likely 6, years. Their usage in engraving tools also dates to early human history.

Later, he showed that bbc africa business report botswana agate an atmosphere devoid of oxygen, diamond is converted to graphite. The dispersion of white light into spectral colors is the primary gemological characteristic of gem diamonds.

bbc africa business report botswana agate

In the twentieth century, experts in gemology have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: Material properties Main articles: Material properties of diamond and Crystallographic defects in diamond Diamond and graphite are two allotropes of carbon: A diamond is a transparent crystal of tetrahedrally bonded carbon atoms sp3 that crystallizes into the diamond lattice which is a variation of the face centered cubic structure.

Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. The difference is that in diamonds, the bonds form an inflexible three-dimensional lattice. In graphite, the atoms are tightly bonded into sheets, which can slide easily over one another. Diamond has a hardness of 10 hardest on this scale.

The diamond hardness depends on its purity, crystalline perfection and orientation: In particular, nanocrystalline diamond aggregates were measured to be harder than any large single crystal diamond. Those aggregates are produced by high-pressure high-temperature treatment of graphite or fullerite C Because it can only be scratched by other diamonds, it maintains its polish extremely well.

Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in engagement or wedding ringswhich are often worn every day.

These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is associated with the crystal growth form, which is single-stage crystal growth.

Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness.

It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges. The toughness of natural diamond has been measured as 2.

As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.

Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band. This conductivity is associated with hydrogen-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments.

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C Diamond has a wide bandgap of 5. This means pure diamond should transmit visible light and appear as a clear colorless crystal.

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Colors in diamond originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron and hydrogen can be introduced into diamond during the growth at significant concentrations up to atomic percents. Transition metals Ni and Co, which are commonly used for growth of synthetic diamond by the high-pressure high-temperature techniques, have been detected in diamond as individual atoms; the maximum concentration is 0.

Virtually any element can be introduced to diamond by ion implantation. Nitrogen is responsible for the yellow and brown in diamonds.

Boron is responsible for the gray blue colors. Plastic deformation is the cause of color in some brown [26] and perhaps pink and red diamonds. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless.

Most diamond impurities replace a carbon atom in the crystal latticeknown as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present. Diamonds of a different color, such as blue, are called fancy colored diamonds, and fall under a different grading scale.Earth mother > Eliseswansborough.

Ya-native-memesjpg (JPEG Image, × pixels) The washing away of Cajun culture - BBC News. Viewpoint: Uncomfortable realities of big game hunting - BBC News. Trophy hunting has been the subject of much media attention amid the backdrop of declining populations of big game animals in Africa.

In May , the IMF country report assessment of the economy of Kiribati is that: “After two years of contraction, the economy recovered in the second half of and inflation pressure dissipated.

Fairburn agate from the Black Hills of South Dakota, 63x The orange bands in this image are from Fairburn agate, a gemstone made of silica (silicon and oxygen). Named after a small town in South Dakota where it is commonly found, the stone is richly coloured by impurities in the rock.

LONDON: BBC World News will be hosting a new series - Africa Business Report - from the end of August The programme, sponsored by Skye Bank, plans to focus on business in Africa, examining the people, businesses and products as well as the issues, challenges and opportunities for companies trading there.

Wine Books Shortlist. The shortlist is a working tool. There still can be a few books added. It is short. The titles of the books are shortened, only a few of the authors are listed, the name of the publisher is short.

A major international priority for Tuvalu in the UN, at the Earth Summit in Johannesburg, South Africa and in other international fora is promoting concern about .

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