Diamond and Tanzanite Jewellery

Published: 05th October 2009
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Diamonds and tanzanite are two types of precious stones which have become increasingly popular in engagement and wedding rings, earrings and pendants. Diamonds and tanzanite are very rare and entire industries are built around mining, grading and selling these precious stones.

Diamonds are durable and valuable because they take millions of years to form in the earth's crust and are the hardest natural material on the planet. The stones reach the earth's surface through volcanic pipes in a rock called "Kimberlite". This rock can be eroded by water and cause diamonds to occur in river beds in what is known as alluvial deposits.

While diamonds have been popular for well over a hundred years, tanzanite is a very recent discovery. The stone was discovered in Tanzania in 1967 and named after its country of origin. Tanzanite has incredible colour properties with hues of blue and purple with hints of red. It is trichroic gem meaning it can exhibit these three colours in one stone when viewed from different directions. The stones are only found in the foothills of Mount Kilimanjaro in Tanzania and are said to be one thousand times rarer than diamonds. When the stones are mined they are brown in colour but once heated, their brilliant blue and purple hues become vivid.

Where they are mined

Diamonds are found in more than 35 different countries globally. These precious stones are found in locations where volcanic activity was previously high. Erosion by natural causes loosened diamonds and deposited the rough stones in the alluvial soil deposits. Streams and rivers are often responsible for unearthing diamonds.

Strip mining is a process where successive layers of the earth's surface are stripped to find possible diamonds. Placer mining involves dredging and sifting alluvial soil deposits in water for diamonds. On the West Coast of Africa, diamond deposits are common on the coastal shorelines and mined with specialised mining and prospecting vessels. Smaller operations also make use of divers submerging themselves to the ocean floor to bring up mineral deposits to be searched for diamonds.

Key diamond mining areas are in Africa, Russia, India, Canada, Australia and the United States of America. In Africa, the most prominent diamond mining country is South Africa which has the Baken, Cullinan, Kimberley, Koffiefontein, the Oaks and the Venetia diamond mines in operation. Other diamond rich countries in Africa include Angola, Botswana, the Democratic Republic of the Congo, Namibia, Sierra Leone and Tanzania.

Tanzanite is very rare for two reasons - it has unmistakable characteristics concerning colour, but is also only found in the Merelani Hills region at the base of Mount Kilimanjaro in Tanzania. Once this area has been mined for an extended period of time (approximately another 20 years) the supply of Tanzanite is likely to run out.

How they are graded

When a precious stone is mined, it is in a physical state known as "rough", meaning that it is uncut and unpolished. Once a diamond or tanzanite has been cut into shape and polished, it is valued to be sold on the jewellery market through a process known as diamond grading and tanzanite grading. The quality of a diamond or tanzanite is governed by the 'four C's', an expression pertaining to the colour, clarity, cut and carat of stones. When a diamond or tanzanite is rated along these specifics, the value of the stone can be determined and it can be used in diamond jewellery and tanzanite jewellery.


The colour of a diamond is transparent but to the naked eye they appear brilliant white with dazzling colours created through light refraction. However, on close inspection, most diamonds have a hint of yellow shading which is rated on a scale of "D" (colourless with no yellow tinge and extremely rare) to "Z" ("M" or lower shows a marked yellow colour in appearance).

The colour of a tanzanite is often its most noticeable quality. A tanzanite stone will be a shade of either blue or violet or both and the dominant shade is listed last on the grading certificate, for example, a stone with dominant blue shades will be described as "violet blue (vB)". The colour scale of grading a tanzanite begins at pale, then light, moderate, intense, and at its strongest is vivid.


Small inclusions (marks) occur in diamonds and tanzanite. The light entering a stone is refracted outwards and adds to the glittery and brilliant quality of these precious stones. A diamond or tanzanite with a lot of inclusions will not refract the light as perfectly as one with little or no inclusions. This affects the beauty of the stone and the price.

A diamond is rated for clarity according to grades. "FL" is the grade given to a flawless diamond with no inclusions visible when checked under magnification (magnification of 10x) to "I" or "P", the grade given to a diamond with inclusions easily visible to the naked eye.

A tanzanite is graded according to similar requirements as diamonds, but with less categories. Grading begins at "LC" (Loupe Clean) which refers to the magnifying tool that graders use to look at stones at a magnification of ten, and that there are no noticeable inclusions. "HI" (heavily included) is the grade given to a stone with many inclusions.


The cut of a diamond or tanzanite refers to the shape that the stone is cut into. When a diamond is cut from a rough stone, the craftsman performing the cutting will need to cut away more than half the stone. Diamonds are cut into specific shapes to allow for maximum refraction of light. Popular cuts are the oval, square cushion, princess, trilliant, heart, emerald, round and pear cuts. The round cut has always been extremely popular and is still to this day. The princess has become very fashionable of late for diamonds whilst tanzanite stones are cut more often according to the other styles.


The carat of a stone refers to the weight and not the size. One diamond carat weighs 200 milligrams, or one fifth of a gram, as does one tanzanite carat.

Increasing popularity

When Diamonds were first discovered, they were a luxury only intended for royalty. For Centuries, kings, queens and other royals were decorated with attractive and opulent jewellery until 1867 when South Africa opened its first diamond mines and everyone had a chance to wear fine diamond jewellery. Since the discovery of Tanzanite just over thirty years ago, the gem has become one of the most popular gems on the planet and is frequently used in jewellery.


Whether these changes are due to economics or aesthetics, diamond and tanzanite jewellery has seen many trends. This can include the cut of stones, how they are set into jewellery and which metals are used to accompany the gems. Bespoke jewellery design has become a very fashionable trend for diamond and tanzanite jewellery. Engagement and wedding rings are still the most popular jewellery for diamonds and tanzanite yet new trends have emerged for the use of diamonds. It has become stylish to buy loose cut diamonds, not only for bespoke jewellery design, but to accessorise cell-phones, sunglasses, watches and other items.

About the Author

Petra Jewellery Design is a bespoke jewellery designer in South Africa specialising in precious stone jewellery as well as diamond grading and tanzanite grading.

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