Rough Diamond — From Kimberlite to Cutting House
Rough Diamond — From Kimberlite to Cutting House
Uncut diamond crystal as recovered from primary or secondary deposits, sorted and traded for cutting or industrial use
Rough diamond is uncut diamond material as recovered from its host deposit, prior to any sawing, bruting, or polishing. The term covers the full range of recovered material — from gem-quality crystal of substantial size to industrial-grade granular bort — and the production, sorting, and trading of rough diamonds is the upstream foundation of the global diamond industry. Rough is mined at primary kimberlite and lamproite deposits and recovered from secondary alluvial and marine deposits; sorted into thousands of grades by size, shape, colour, and clarity; and distributed through structured allocation systems and open trading markets to the cutting centres of Antwerp, Mumbai-Surat, Tel Aviv, and elsewhere.
Production and sources
Primary diamond rough is recovered from kimberlite pipes — vertical igneous intrusions that brought diamond crystals to the upper crust from depths of 150 kilometres or more — and from related lamproite host rocks. Major primary producers include the Botswana mines (Jwaneng, Orapa, and others) operated by Debswana, the Russian deposits (Mir, Aikhal, Udachny, and others) operated by ALROSA, the Diavik and Ekati mines in Canada's Northwest Territories, the Venetia mine in South Africa, and the historical Kimberley group of mines that gave the host rock its name.
Secondary deposits — alluvial gravels and beach placers in which diamonds have been concentrated by erosion of primary host rocks — are worked extensively in West Africa (Sierra Leone, Liberia, Ivory Coast), in the Democratic Republic of the Congo, in Angola, and in marine environments off the southern African coast. Secondary deposits typically yield well-formed, clean rough because crystals weakened by inclusions or surface flaws have been destroyed by transport.
Annual global production runs in the range of 110 to 130 million carats, of which gem-quality material represents approximately 20 to 30% by weight but a much larger share by value. Industrial-grade diamond constitutes the balance and is used in cutting, drilling, and polishing applications across the industrial economy.
Sorting and grading
Rough diamond sorting is a specialised trade in its own right. Material is divided into thousands of categories along multiple dimensions: size (typically by sieve grade in fractions of a carat or in points), shape (sawables, makeables, cleavages, flats, irregulars), colour (white, off-white, fancy yellow, fancy brown, and the rare fancy colours), clarity (the presence and severity of inclusions), and surface quality (smooth crystal faces versus etched or fractured surfaces). Major producers maintain in-house sorting operations capable of processing hundreds of grades simultaneously; specialist sorting houses offer the same service to smaller producers.
The end result of sorting is a parcel — a collection of individual rough stones grouped by category — that can be valued, sold, and allocated to cutting operations. Parcel valuation is a skill that takes years to acquire; the De Beers and ALROSA sorting operations are widely considered the most refined in the trade and serve as informal benchmarks for the global market.
Trade structures
Rough diamond trade is structured around two principal mechanisms. The producer-allocation systems — De Beers' Sights, the ALROSA Sales Cycles — provide regular allocations of pre-sorted parcels to a limited group of qualified buyers (Sightholders for De Beers) who commit to taking what is offered at the negotiated price. The open market — primarily through tender sales, exchanges in Antwerp and Dubai, and direct producer-to-cutter relationships — handles the balance of production and operates on conventional bid-and-offer logic.
The Kimberley Process Certification Scheme, established in 2003, requires shipments of rough diamonds in international trade to be accompanied by certificates of origin attesting that the goods have not been used to finance armed conflict against governments. The scheme has substantially reduced — though not eliminated — the trade in conflict diamonds and operates under voluntary participation by producing and trading countries.
From rough to polished
Cutting houses receive rough parcels and proceed through stages of planning (using laser-based imaging to model optimal facet placement), sawing or laser cutting (to divide larger crystals), bruting (rounding the girdle for round-brilliant production), and faceting and polishing. Yield from rough to polished varies from roughly 30% to 60% depending on the stone's shape, inclusions, and the cut style chosen; well-formed, clean rough yields more, while heavily included or oddly shaped material yields less.