Written by Carolyn Doyle for customers of
The Dorado Company
and other visitors to the azgem.com website who subscribe.

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Usable Gems... and a little opinion.

Gemstone Rough

Specifically, she asks... "I've read in your newsletter where you speak of gemstone rough. How is that different from the gems you sell?"

Think of it as "before and after"

Gem rough is the gem crystal as it comes from the mine, before it is fashioned into a faceted or cabochon cut gem.

Gem rough is a term usually applied to colored gems such as emerald, sapphire, and in the case of the photo above, aquamarine. Diamonds and diamond rough are generally referred to by those names.

Gem rough comes from the mines in a wide variety of qualities and sizes, as you would expect. Quality and size can be relative to the gem involved. For example tsavorite (the beautiful rich green variety of garnet usually occurs in sizes under two grams. Colors can range from emerald green to a blackish green.

The miner is the first player in sorting and grading gem rough. Even parcels of "mine run" gemstone rough is graded by quality, and possibly by size. 

The general grades of gem rough are:

	Facet grade
	Cabochon grade
	Bead grade

The Dorado Company was (until recently) involved in gem mining in Madagascar. We are currently working to partner with the owner of several existing gem mines in East Africa.

Our interest is in facet grade gem rough. Lower grades of rough are sold off locally.

The larger the piece of rough, and the more pleasing the color, the more valuable it is to a gem cutter, simply because of the finished gem that can be produced from that piece of rough..

Many types of gem crystals can grow to large sizes. Amethyst, citrine, spinel, and aquamarine are examples.

Clarity is also important to the value of a finished gem, and therefore to the gem rough that the cutter starts with. Inclusions such as veils, needles, and small crystals of other minerals must be eliminated in the cutting process to the extent possible.  

Amethyst and many other gems with eye-visible inclusions have a greatly diminished value. 

Inclusions are more acceptable and expected in some other gems such as emerald. This is because emerald crystals generally occur with many inclusions. The demand and market value of emeralds dictates that gems with some inclusions are accepted. Even here, the prominence of inclusions impacts the value of the finished emerald.

Cutters are looking for other good characteristics in the gemstone rough they buy and cut. In addition to the size of the rough, cutters evaluate the shape of the piece of rough. A "chunky" shape generally yields a larger finished gem to the cutter.

Before faceting a piece of rough, the cutter will "preform" the piece by grinding away inclusions and voids near the surface of the piece of rough, and give it the general shape of the finished gem.

The piece can then be faceted and polished to yield a beautiful finished gemstone.

 

 

 

Gem Industry News...

 

478 Carat Gem Quality Diamond Discovered

 

Gem industry news sources are reporting the discovery of a huge diamond crystal of exceptional quality.

Miners in the Kingdom of Lesotho have found one of the world's largest diamonds, a near-flawless white gem weighing nearly 500 carats.

The diamond was reportedly discovered in the Letseng Mine on September 8. It has been analyzed by experts in Antwerp and found to weigh 478 carats, with very few inclusions and of outstanding color and clarity.

The company said "It has the potential to yield one of the largest flawless D color round polished diamonds in history," the mining company said.

The Letseng diamond mine is the world’s highest operating mines, located at approximately 10,000 feet above sea level. The mine is a 70-30 partnership between Gem Diamonds the government of Lesotho.

Letseng is one of the most productive mines in history. Four of the world's 20 largest rough diamonds have been found at this mine, including the three largest found in the last 100 years.

Before the piece of rough is cut into gems it is hard to value. A similar weight stone with lesser-quality color and clarity has recently sold for $12 million.

The world's largest diamond is the Cullinan, discovered in South Africa in 1905. It weighed more than 3,100 carats before it was cut into more than one hundred separate gems.

The Letseng Mine is 70 percent owned by Gem Diamonds Limited and 30 percent owned by the government of Lesotho.