Our Diamonds

The Letšeng mine in Lesotho produces the highest quality gem diamonds, consistently achieving the highest price per carat of any kimberlite mine in the world. It is also famous for its large top colour white diamonds, and has produced four of the 20 largest white diamonds ever recorded since Gem Diamonds took the mine over in 2006.

The Lesotho Legend

Famous Letšeng Diamonds

The ultimate gem

Diamond types are classified by nitrogen content, namely Type I and Type II. Type I diamonds contain nitrogen while Type II diamonds are nitrogen free and are usually white or blue. Type IIa and Type IIb (blue colour) are very rare and generally thought to comprise less than 1% of all diamonds. While it is possible to obtain D Flawless diamonds from Type I diamonds, the most sought after diamonds are Type IIa Flawless diamonds. Type II diamonds have superior optical properties and have a superior overall polish to Type I diamonds.

In ancient times, incredible white diamonds were recovered in Golconda in India, and to this day Golconda diamonds have held a superior position to white diamonds produced anywhere else in the world. However, notwithstanding these Golconda gems, the Gem Diamonds Marketing Consultants and some of the world's leading Diamantaires believe that the D Flawless diamonds from Letšeng are the prize gems of them all.

Rough gem quality diamonds

These diamonds are attractive when viewed and are the easiest diamonds to manufacture and polish for jewellery.

The value of a diamond is based on rarity.

Gem quality diamonds are based on the combination of the following characteristics:


To a large degree size does matter, especially with large white D, E F & G colours. However, when dealing with rare fancy colours such as reds, blues, oranges and greens, even small stones are highly prized gems.


A range of colourless, moving to lighter yellows and browns are regarded as gem colours. The closer a diamond is to colourless, the more valuable it becomes. Deeper colours of yellow and brown, as well as rare colours such as orange, violet, purple, green, pink, blue and red are referred to as fancy colours.


Originally gem quality rough diamonds were those diamonds without cracks, twins or large inclusions, the equivalent of the polished grade SI3 or better. Lesser qualities were referred to as near-gem and included low clivage and semi-opaque rejection material.

In today's terminology, the better near-gem qualities are included as gem quality, as it is now viewed that any diamond which can provide a polishable gem be included, regardless of the fact that more splits (sawing, cleaving or lasering) are required to achieve polishable pieces.


The most desired rough gem shapes are the following:

  • crystals (Sharp edged octahedrons),
  • octahedrons with some rounding to the edges and points
  • dodecahedrons
  • triangular maccles
  • rounded dodecahedral maccles
  • shapes that have high yielding forms either for rounds or fancy cuts

Less desirable gem shapes are cubes, irregular low yielding shapes and twinned or aggregated forms.

Other factors which influence the overall gem description would include stones with unattractive clouds, milkiness or colour banding/zoning.

Therefore, the most desired rough gem diamonds would be those having good colour, shape and internal clarity, without ignoring the size factor.

Polished gem diamonds

Based on the descriptions, a polished gem diamond requires the basic 4 C's:

Carat weight

Larger diamonds are rare. The size of the polished gem does matter and is further complicated by reaching stipulated price bands, such as 0.25ct, 0.50ct, 1.00ct, 3.00ct, 5.00ct, and 10.00ct and so on. The price difference between a 0.99 carat and a 1.00 carat is very high and this continues throughout all the size bands.


Diamonds come in many different colours. The colour of most diamonds range from colourless to light yellow or brown. Normal diamonds are graded on a colour scale which ranges from D (colourless) to Z (light yellow). Within this range colourless diamonds are the most rare, and the most valuable. Diamonds that are blue, pink, purple, orange, red, green or canary yellow are called "fancy colours", and are very rare.


The clarity of a polished diamond is the relative absence of inclusions or blemishes. The top clarity grade is "Flawless" and diamonds graded as such are rare. The clarity of a diamond has a direct influence on the value of a polished diamond. Therefore, the higher the clarity, the more prized and expensive the polished gem becomes.


Round Brilliant cut diamonds are more expensive than fancy shaped diamonds. This is because in the polishing process more weight is lost when polishing a Round Brilliant than when polishing a fancy shape as the latter is polished to maximise the polished weight recovered from the rough diamond.

Other important factors for polished gem diamonds

Quality of polish

It is estimated that of all the diamonds mined only 0.001% will produce D Flawless finished stones. [Bryan Boyne, G.G. (GIA)].

The quality of polish and symmetry is vital to achieve maximum brilliance, scintillation ('sparkle') and dispersion ('fire').