How are gem diamonds valued?

Diamonds are crystals of pure carbon that have been subjected to tremendous pressure and heat deep within the Earth's crust, and come to the surface through volcanic eruptions.

Dance of light

The brilliance of a diamond results from refraction, reflection and dispersion of light ... kind of like light dancing in the diamond.

A ray of light passing through a diamond facet (one of many small planes cut onto its surface) is refracted (or bent). The bent ray is reflected back and forth inside the diamond before it "escapes" through a top facet (in a well-cut diamond). Most diamonds have 58 facets.

In refraction each colour of the ray is bent at a slightly different angle. This separation of light into colours (or spreading of colours) is called dispersion. The ray of light is emitted as a glittering rainbow. This ability of the diamond (like the prism) to split white light into its component colours has made it the world's favourite jewel.

Hardest natural substance

The diamond is the hardest natural substance found on Earth. Because of its hardness, the diamond is used for cutting, grinding, and boring other hard materials. The saying, "it takes a diamond to cut a diamond" is true. Diamonds are employed by gem cutters to shape and polish diamonds and other gems.

Hardness denotes resistance to scratching. It does not mean the diamond is indestructible. A diamond can be cleanly broken with a sharp, accurate blow because of its cleavage. Cleavage is the tendency of crystalline minerals (such as diamond) to break along defined parallel planes producing flat, even surfaces.

4 C's

Gem diamonds are valued according to the 4C's - carat, clarity, colour, and cut.

  • CARAT - The weight of a diamond is measured by the carat. One carat equals 0.2 gm.

    The price per carat does not increase proportionately with increasing size. Instead, there are sharp jumps around milestone carat weights. Therefore, a diamond of 5 carats is worth more than five 1-carat stones of the same quality.

  • CLARITY - The clarity of a diamond can be lessened by various kinds of imperfections. Among these imperfections are inclusions (other substances enclosed in the crystals), small bubbles, and small fissures or cracks.

  • COLOUR - The best-quality diamonds (and the most valuable) are completely colourless ... allowing white light to pass through and be dispersed as rainbows of colour. Very few diamonds reach this standard.

    Most diamonds are tinged with colour. If a diamond's colour is sufficiently intense, it is prized as a gem and called a "fancy". Blue and pink diamonds are the most valuable. Red diamonds are very rare. Many diamonds have a yellowish tint caused by the presence of tiny amounts of nitrogen.

  • CUT - A well-cut diamond will internally reflect light from one facet to another and finally disperse it through a top facet of the stone. Diamonds that are cut too deep or too shallow lack brilliance because light escapes through the sides or bottom.

"George Files" by Parenting the Next Generation