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Antoinette Corbishley
11th January 2008 15:58

What is a diamond?

 

What is a diamond?

Diamonds are an amazing mineral and being at least 990,000,000 years old and many around 3,200,000,000 years old (3.2 billion years)! I thought I'd share with you a little bit about them.

Diamond is a mineral found deep within the earth's surface, and is one of two crystalline forms of the element Carbon (the other being graphite). Diamonds are formed at depths of around 90 miles or more in volcanic pipes within the Earth's surface, at this depth the carbon is under pressures of approximately 5 gigapascals and a temperature of roughly 1200 degree Celsius transforming it into diamond. The longer a diamond is exposed to this intense heat and pressure, the larger the diamonds cubic crystal structure grows.

A diamonds crystal system is Isometric (cubic) and because of the uniform arrangement of their constituent carbon atoms, diamond crystals are well-formed - usually octahedral with rounded edges and slightly convex faces.

So how do the diamonds reach a depth at which they can be mined?

The magma found in the volcanic pipes where the diamonds are formed acts like a lift carrying the diamonds to the surface during a volcanic eruption, the magma, the formed rocks and crystals from this blast can be distributed over a large area. This volcanic layer or pipe is known as the primary source, and this is where the diamonds are mined from (diamond deposits in river gravels are classed as secondary sources).

Diamonds are essentially inclusions in the volcanic rock Kimberlite, the Kimberlite magma is usually much younger than the diamonds they carry.

The first country to mine for this amazing mineral was India, the most well know diamond discovered near Hyderabad being the Koh-i-noor, which means ' mountain of light', know since 1304. For the past 150 years the Koh-i-noor weighing 106 carats, has been part of the British Crown Jewels.

The Koh-i-nur diamond came from the Treasury at Lahore in the Punjab and was re-cut for Queen Victoria in 1852. Traditionally the Koh-i-nur is only worn by a queen or queen consort: it is said to bring bad luck to any man who wears it.

Where are diamonds mined?

Australia is the main diamond producer today, and if we look to our Diamond map we can see other producing countries include South Africa, Ghana, Sierra Leone, Zaire, Botswana, Namibia, the former USSR, the USA, Canada and Brazil.

Also it is believed by some scientists that diamonds may exist in large quantities on Neptune and Uranus.

How did diamond get it's name?

The name diamond derives from the Greek asamas, which means invincible. The carbon atoms in a diamond are linked together as a three dimensional network giving it its amazing hardness, (unlike graphite where the carbon is linked into sheets therefore making graphite very soft and placing it right at the other end of the scale). With a hardness of ten on the moh's scale diamond is the hardest mineral on Earth, making it invaluable to industry and with its exceptional luster and incomparable fiery brilliance the most highly prized gem of all.

Their popularity has increased greatly since the 19th century due to better cutting and polishing techniques, improved supply and from their association with love. Also around this time gemologists developed the characteristics for a cut diamond which we know as the four C's - Cut, colour,Clarity and Carat.

Clarity- Out of the four C's, Clarity effects the cost of the stone more than anything (obviously in relation to the size), as the clearer the stone the better the stone sparkles due to more light able to pass through the stone, and bounce off its facets. A flawless diamond will have a lively play of light and high brilliance, at the other end of the scale the diamond will look dull and lifeless, as the light cannot pass through the stone easily due to the high number of inclusions, cracks, or natural features within the stone. We look for inclusions with the stone through a x10 loop - this magnify's the impurities in order to grade the stone.

We here at Harriet Kelsall Jewellery Design tend to use SI clarity diamonds as we find these are a good sparkly stone where any inclusions aren't visible to the naked eye, so unless looked at by a gemologist the stone looks both beautiful and isn't so high up the grading scale that it breaks the bank. Harriet herself has H SI quality diamonds in her engagement ring, and she works with diamonds every day.

FL = Flawless (a diamond completely free of inclusions)

IF = Internally Flawless (the table of the stone is completely clear)

VVS1 and VVS2 = Very Very Slight inclusions (very, very small inclusions are only visible with very considerable to great difficulty when looked at through a x10 loop by an experienced gemologist. The distinction between VVS1 and VVS2 is determined by the number, size and position of inclusions)

VS1 and VS2 = Very Slight inclusions (very small inclusions ranging from not too difficult to easy to spot through a x10 loop by an experienced gemologist. The distinction between VS1 and VS2 is determined by the number, size and position of inclusions)

Sl1 and SI2 =Slight inclusions (small inclusions which are easy to spot through a x10 loop by an experienced gemologist. The distinction between SI1 and SI2 is determined by the number, size and position of inclusions)

I1 = Included or also know as "first pique"(inclusions which are difficult for an experienced gemologist to spot with the naked eye when examining through the crown of the stone, but very easy to see when using a x10 loop)

I2 = Included or second "pique" (large and or numerous inclusions which are easy to spot by an expert with the naked eye. These inclusions will effect the brilliance/sparkle of the stone)

I3 = Included or "third pique" (large and or numerous inclusions which are very easy to spot with the naked eye. These inclusions will effect the brilliance/sparkle of the stone).

Colour - Diamond colour grading starts at D (D being the whitest) right the way down the alphabet to Z, the lower down the alphabet the yellowier or browner the stone, this is usually due to the presence of Nitrogen the most common impurity present, which replaces a very small amount of atoms in the diamonds structure and causes the discoloration from blueish-white to white to silver to yellow etc. Most high street jewellers use I colour, we at HKJD tend to go up a grade to H colour diamonds, but anything above an I is classed as a nice white stone that doesn't draw colour. To the untrained eye it isn't easy to tell the difference unless the colour graded diamonds are lined up next to each other making the difference more obvious.

As well as the traditional white you can also buy coloured "Fancy" diamonds, most have been heat treated to enhance their colour, but coloured diamonds do occur naturally but are generally a lot more expensive, especially pink or red diamonds which are extremely rare.

Examples of pink and red diamonds can be seen in both of our showrooms is a pink diamond ring we have at our Cambridge shop or see which is here at our Halls Green studio.

Cognac diamonds are popular as they have warmth as well as the all important sparkle. Other available diamond colours are black, ocean blue, sky blue, ice blue, (natural blue diamonds contain the element boron (B), which changes the conductivity of the diamond) forest green, apple green, olive, orange, cognac, gold, canary yellow, natural canary (natural yellow diamonds contain the element nitrogen (N)).See Harriett's blog for more information www.hkjewellery.co.uk/blog/default.asp?Entry=19> and examples of coloured diamonds used in jewellery.

Cut - Refers to the brilliance of the diamond and how it has been facetted and polished from its original rough form to the final gem stone proportions, and the angle the stone is cut which is often confused with shape. The cut facets are positioned in order to maximize the fire and brilliance of the stone. The fire within a diamond refers to the dispersion of light which is a result of the placement of the faces on the crown of the diamond taking advantage of the prism effect which is seen as rainbows and glints of colour.

The most well know cut today is the round brilliant, developed in 1919 by Belgin born Marcel Tolkowsky a mathematician and gem enthusiast. He calculated the ideal shape a diamond should be to return and scatter the light when the stone is looked at from above. The modern day brilliant cut diamond has 57 polished facets, 33 of these are on the crown of the stone, and 24 on the pavilion, see diagram below. The crown's function is to distribute the light, while the pavilions' purpose is to reflect the light back through the top of the diamond to create maximum sparkle.

Most diamonds are cut in Amsterdam; examples are of the most popular cuts used: Round, Oval, Pear, Marquise, Heart, Princess, Asscher, Emerald, Radiant

Carat - Carat refers to how much the diamond weighs i.e. its mass, the value of a diamond increases dramatically the heavier the stone is and its subsequent rise in carat weigh. Very sensitive weighing scales are used to measure carat weight.

Some of the most famous diamonds in history are the previously mentioned Koh-I-Noor weighing 186 carats and took 38 days to cut.

The Hope Diamond was a blue diamond weighing 44carats

And last but not least The Taylor-Burton Diamond originally known as the Cartier weighing in at a mere 69 carats

Other interesting facts about diamond: Diamond is reputed to promote prosperity, generosity, love and spirituality. Only 20% of diamonds mined are gem quality the remainder are used in industry.

Diamonds are such a huge subject I have only skimmed the surface but I hope what I have covered you have found interesting!

Antoinette Corbishley
 

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  • Harriet Kelsall Jewellery Design, North Barn, Fairclough Hall Farm, Halls Green, Weston, Hertfordshire, SG4 7DP, England
    Phone: +44 (0)1462 790565 Fax: +44 (0)1462 790140 enquiries@hkjewellery.co.uk
  • Harriet Kelsall Jewellery Design, 6/7 Green Street, Cambridge, Cambridgeshire, CB2 3JU, England.
    Phone: +44 (0)1223 461333 Fax: +44 (0)1223 365269 cambridge@hkjewellery.co.uk

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