Close inspection of the 37,555-gram (187,775 carat) cluster reveals that it contains very little matrix or other minerals, meaning the piece is almost entirely made up of emeralds, which, given its sheer size and formation, makes this a very rare find indeed.

The Kafubu Cluster, our gentle giant, is a testament to the high-quality gemstones that can be produced when Mother Nature allows time for the various crystals to form deep within the Earth’s crust. Gemfields’ geologists describe the formation process of emeralds as an incredibly rare coming together of uncommon elements in unusual circumstances.

A precise set of remarkable geological and geochemical conditions is required for the formation of these brilliant green gems. Beryllium, essential for the crystallisation of beryl, is one of the most elusive elements in the Earth’s crust (estimated to be about 2 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 (ultramafic) rocks in order to attain the desired colour. Not all pegmatites are beryllium-bearing and even fewer are emplaced within rocks that contain adequate chromium. These factors – coupled with even more specific temperature, pressure and fluid content requirements for its formation – makes emerald extremely rare and remarkably erratic in its distribution.

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 and most exceptional emeralds ever found, of which the Kafubu Cluster is an extraordinary example.

Just like Michelangelo was a “subtractive sculptor”, our geologists at Kagem have “freed the emerald crystals from their host rock”. The result is a large mass, filled with numerous individual and intertwined emerald crystals, displaying their perfect hexagonal structure.

Jackson Mtonga, Kagem Assistant Sort House Manager, who has 28 years of experience of emerald discoveries at Kagem, paid testimony to the incredible nature of this find: “Rarity is one of the factors that makes emeralds hold such a special value in many cultures around the world, but the combination of this crystal cluster formation, the overall quality and the sheer enormity of the Kafubu Cluster is something I never thought possible.”

The Kafubu Cluster displays all the desired characteristics that an emerald should possess: a vivid green colour overall that glows and shines. It offers different levels of perfect crystallisation, to allow the future cutter to create a collection of gems, from fine quality faceting material to cabochons and beads for everyday fun. It is possible that a customer may decide to preserve this in its natural form or cut the piece to yield tens of thousands of carats of commercial to fine quality cut emeralds.

The Kafubu Cluster is being offered for sale at Gemfields’ upcoming emerald auction, with viewing from 31 October and bidding closing on 17 November. Given its size and quality, it is likely that the Kafubu Cluster will be the most expensive single emerald piece ever sold by Gemfields.

The naming of uncut emeralds is a tradition reserved only for the rarest and most remarkable gems. 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 carats. Unlike Insofu (elephant), Inkalamu (lion) and Chipembele (rhino), the Kafubu Cluster is not one single crystal and is completely unique in character. As such, it calls for a name as inimitable as it is.

The Kafubu Cluster was discovered in the Chama pit of the Kagem emerald mine, based in Lufwanyama in Zambia. Kafubu is a river which forms the natural boundary of Kagem in the southern part of the Kagem licence, and it is from this that the Kafubu Cluster takes its name – honouring the unique landscape in which it was formed. Kagem is believed to be the world’s single largest producing emerald mine; it is 75% owned by Gemfields, in a model partnership with the Zambian government.