Gemstone miner Gemfields is set to put on auction the 187 775 ct (37 555 g) cluster of emeralds that was unearthed in the Chama pit of the miner’s 75%-owned Kagem emerald mine, in Zambia, in March 2020.

Viewings of the cluster opened on October 31, with bidding to close on November 17.

Given its size and quality, Gemfields says the Kafubu cluster will likely be the most expensive single emerald piece it has ever sold.

The cluster takes its name from the Kafubu river, which forms the natural boundary of Kagem in the southern part of the mine licence.

Gemfields says close inspection of the cluster reveals “very little” matrix or other minerals, meaning the piece is almost entirely made up of emeralds.

Gemfields’ geologists describe the formation process of emeralds as an “incredibly rare coming together of uncommon elements in unusual circumstances”.

Kagem assistant sorthouse manager Jackson Mtonga – with 28 years’ experience in emerald discoveries at Kagem – says rarity is one of the factors that makes emeralds hold such a special value in many cultures around the world.

He adds that the combination of this crystal cluster formation, the overall quality and the sheer enormity of the Kafubu cluster, is something he never thought possible.

Gemfields says it is possible that a buyer may decide to preserve the Kafubu cluster in its natural form or cut the piece to yield tens of thousands of carats of commercial- to fine-quality cut emeralds.

Meanwhile, Gemfields points out that the naming of uncut emeralds is a tradition reserved only for the rarest and most remarkable gems. The miner says that, while no official record exists, it is thought that no more than two dozen gemstones have ever been given their own name, and it is “extremely unusual” to encounter a gemstone weighing more than 1 000 ct.

Unlike the 6 225 ct Insofu (meaning elephant), the 5 655 ct Inkalamu (meaning lion) and the 7 525 ct Chipembele (meaning rhino), the Kafubu cluster is not one single crystal and, therefore, is completely unique in character, states Gemfields.

GEMSTONE FORMATION
Gemfields explains that a precise set of geological and geochemical conditions are required for the formation of green gemstones.

Beryllium – essential for the crystallisation of beryl, is one of the most elusive elements in the Earth’s crust (estimated to be about two parts per million) and must be carried up to the surface by pegmatites, which, in turn, must come into contact with chromium and vanadium-bearing rocks to attain the desired colour.

These factors – coupled with even more specific temperature, pressure and fluid content requirements for its formation – make emerald extremely rare and remarkably erratic in its distribution.

Gemfields also notes that Zambian emeralds tend to have a higher iron content than emeralds from other origins, which means they are less fragile. High iron content also means fewer surface-reaching fractures and less need for treatments and enhancements.

The careful process of recovering emeralds by hand at the Kagem emerald mine has enabled the safe recovery of some of the largest emeralds ever found.