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Diamonds for Everyone

Diamond History By Diamond Jewellery Wholesaler

Diamonds formed in cratons

The conditions for diamond formation to happen in the lithospheric mantle occur at considerable depth corresponding to the aforementioned requirements of temperature and pressure. These depths are estimated to be in between 90-120 miles (140-190 kilometers) though occasionally diamonds have crystallized at depths of 300-400 km as well. The rate at which temperature changes with increasing depth into the Earth varies greatly in different parts of the Earth.

In particular, under oceanic plates the temperature rises more quickly with depth, beyond the range required for diamond formation at the depth required. The correct combination of temperature and pressure is only found in the thick, ancient, and stable parts of continental plates where regions of lithosphere known as cratons exist. Long residence in the cratonic lithosphere allows diamond crystals to grow larger.

djewels The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral. Its lustrous faces also indicate that this crystal is from a primary deposit.

Through studies of carbon isotope ratios (similar to the methodology used in carbon dating, except with the stable isotopes C-12 and C-13), it has been shown that the carbon found in diamonds comes from both inorganic and organic sources. These two different source carbons have measurably different 13C:12C ratios. Diamonds that have come to the Earths surface are generally very old, ranging from under 1 billion to 3.3 billion years old.

Diamonds and Meteorite

Diamonds can also form in other natural high-pressure, relatively low-temperature events. Very small diamonds, known as microdiamonds or nanodiamonds, have been found in impact craters where meteors strike the Earth and create shock zones of high pressure and temperature where diamond formation can occur. Microdiamonds are now used as one indicator of ancient meteorite impact

Surface Properties

How is diamond like a freshly waxed car? It repels water, an unusual property for a mineral. Diamonds strong bonding and carbon composition cause its surface to repel water but to readily accept wax and grease.

These two properties provide an effective means of separating diamonds from other minerals that come out of mining operations. Washed gravel containing diamonds is flushed with water over a sloping surface covered with a mixture of wax and grease, a "grease table." The diamonds stick to the table, while the wetted waste minerals wash over it. Gem diamonds readily pick up a greasy film, but cleaning with ammonia or a good detergent restores their brilliance

Gemological characteristics

The most familiar usage of diamonds today is as gemstones used for adornment. This usage dates back into antiquity and predates other uses.The dispersion of white light into spectral colors, is the primary gemological characteristic of gem diamonds. In the twentieth century, experts in the field of 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: these are carat, cut, color, and clarity.

There are three major non-profit gemological associations which grade and provide reports on diamonds. While carat weight and cut angles are mathematically defined, the clarity and color are judged by the trained human eye and are therefore open to slight variance in interpretation.

Gemological Institute of America (GIA) was the first laboratory in America to issue modern diamond reports, and is held in high regard amongst gemologists for its consistent, conservative grading.

American Gemological Society (AGS) is not as widely recognized nor as old as the GIA but garners a high reputation. The AGS employs a number system for grading cut quality, color grade, and clarity. The highest grade being 0, and the lowest being 10.

Diamond High Council (HRD) Official certification laboratory of the Belgian diamond industry, located in Antwerp. Antwerp World Diamond Center

The Famous 4 Cs

Carat

The carat weight measures the mass of a diamond. One carat is defined as 200 milligrams (about 0.007 ounce avoirdupois). The point unit-equal to one one-hundredth of a carat (0.01 carat, or 2 mg)-is commonly used for diamonds of less than one carat. All else being equal, the price per carat increases with carat weight, since larger diamonds are both rarer and more desirable for use as gemstones.

The price per carat does not increase smoothly with increasing size. Instead, there are sharp jumps around milestone carat weights, as demand is much higher for diamonds weighing just more than a milestone than for those weighing just less.

As an example, a 0.95 carat diamond may have a significantly lower price per carat than a comparable 1.05 carat diamond, because of differences in demand.

Clarity

The clarity of a diamond refers to how clear, or "clean" the diamond is. The more "clean" the diamond, the higher the price. Most diamonds have "imperfections" in them. The clarity scale is a measure of the severity of those imperfections or "inclusions" as it is known in the trade.

Both of these distinguishable features together are called clarity characteristics. A clarity grade is determined by the relative absence of clarity characteristics.

The following is the GIA Diamond clarity-scale:

(FL) FLAWLESS

Shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader

(IF) INTERNALLY FLAWLESS

Has no inclusions when examined by an experienced grader using 10X magnification, but will have some minor blemishes

(VVS1 and VVS2) VERY VERY SLIGHTLY INCLUDED

Contains minute inclusions that are difficult even for experienced graders to see under 10X magnification.

(VS1 and VS2) VERY SLIGHTLY INCLUDED

Contains minute inclusions such as small crystals, clouds, or feathers when observed with effort under 10X magnification.

(SI1 and SI2) SLIGHTLY INCLUDED

Contains inclusions (clouds, included crystals, knots, cavities, and feathers) that are noticeable to an experienced grader under 10X magnification.

(I1, I2, I3) INCLUDED

Contains inclusions (possibly large feathers or large included crystals) that are obvious under 10X magnification and may affect transparency and brilliance

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