Diamond

1. 02.02 · Stones

   Diamond types and black diamonds

   Type Ia diamonds, more than 95% of natural stones, hold nitrogen in aggregates. Type Ib diamonds, a rare few, contain isolated nitrogen atoms and are almost always brown, yellow or orange. Type IIa diamonds have no easily measurable nitrogen or boron; the Golconda region of India is their historic source. Type IIb diamonds contain boron, which gives them their blue or gray color and their electrical conductivity; most come from India and the Cullinan mine in South Africa. Laboratories also use type as an early clue when screening for treatment or laboratory growth.

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2. 03.10 · Science

   Nitrogen, boron and diamond types

   Type II diamonds have no nitrogen detectable by FTIR, and they too occur very rarely in nature. Type IIa stones are often exceptionally colorless, and the largest gem diamonds, the Cullinan-like stones that formed 360 to 750 km down, routinely qualify as IIa. Type IIb diamonds contain boron, which colors them blue or gray and makes them electrically conductive. Type matters in practice: IIa is the usual type of CVD-grown diamond and the type HPHT treatment can decolorize, so IIa stones are routinely referred for laboratory testing.

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3. 05.02 · Mining

   Diamonds in Africa

   South Africa’s modern industry began at Kimberley, where miners dug the Big Hole between 1871 and 1914. Cullinan, now owned by Petra Diamonds, produced the 3,106.75 ct Cullinan diamond in 1905 and is the only significant source of blue diamonds. In Namibia, marine operations supply more than three-quarters of production. Angola’s Catoca pipe is owned 59% by the state company Endiama; the other 41%, formerly held by the sanctioned Russian miner Alrosa, passed to an Omani investor in November 2024. Around Mbuji-Mayi in the Democratic Republic of the Congo, diggers work vast deposits once dominated by the state company MIBA. In Sierra Leone, the Koidu kimberlite mine halted in 2025 after a labor dispute, idling the country’s largest diamond company; national output fell from 573,983 carats in 2024 to 121,620 in 2025.

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4. 06.06 · Industry

   Diamond trading and cutting hubs

   Ramat Gan, beside Tel Aviv, holds the Israel Diamond Exchange. In New York, the district on 47th Street between Fifth Avenue and Avenue of the Americas is organized around the Diamond Dealers Club, whose roughly 1,800 members handled more than 95% of the diamonds imported into the United States according to a 2009 law review study. The Dubai Diamond Exchange sits inside the DMCC free zone, which recorded US$41.7 billion of diamond trade in 2025 against US$38.3 billion in 2023 and calls itself the largest platform for diamond tenders. Hong Kong serves Asia as a polished and jewelry market and hosts the HKTDC Hong Kong International Jewellery Show each March, which drew 2,353 exhibitors and 51,054 buyers in 2026.

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5. 12.04 · Instruments

   Diamond testers

   Synthetic moissanite defeated the test in the late 1990s: GIA reported that thermal probes react to it as if it were diamond. GIA gives diamond a thermal inertia of 0.55 to 1.7 and moissanite 1.6 to 4.8 in cal/cm C, ranges that overlap. Later multi-testers added electrical conductivity, since moissanite is a semiconductor. That cross-check has its own trap: boron-bearing type IIb diamond conducts too, and GIA reports that over 80% of colorless HPHT laboratory-grown diamonds submitted to it since 2020 are type IIb, so a conductive reading is not proof of moissanite. A loupe helps only if used correctly. Moissanite is cut with its c-axis perpendicular to the table, so face-up it shows no doubling; tilt it and look in at an angle and the back facet junctions double. It is also lighter, 3.22 against diamond’s 3.52.

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6. 13.11 · Markets

   Colored stones and diamonds compared

   Colored stones have no common price list, their prices depend heavily on origin and treatment, and the market is watched mainly through dealer guides and auction results. The longest comparison built from completed transactions comes from Luc Renneboog and Christophe Spaenjers, who used 3,952 Sotheby's and Christie's lots sold between 1999 and 2010 to build separate indices for white diamonds, colored diamonds and other gems. Average real returns in US dollars over the full period were 6.4% a year for white diamonds and 2.9% for colored diamonds, against 11.6% for gold and −0.1% for equities. From 2003 the figures were 10.0% for white diamonds, 5.5% for colored diamonds and 6.8% for other gems. Auction lots are drawn from the top of the market, so they describe what exceptional stones did, not what an average buyer would have seen.

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7. 17.01 · Ethics

   Conflict diamonds in Sierra Leone, Angola and Liberia

   In Angola, the UNITA rebel movement is estimated to have earned US$600 to 700 million from diamonds between 1992 and 1994. The UN Security Council banned purchases of Angolan diamonds lacking government certificates in June 1998, and Global Witness’s December 1998 report A Rough Trade named the companies and governments involved. In Sierra Leone, the RUF rebel group held diamond areas during a civil war from 1991 to 2002 that killed about 75,000 people and became notorious for the mutilation of civilians. Neighboring Liberia, under President Charles Taylor, traded weapons for RUF diamonds and exported them as its own, and the Security Council banned Liberian rough diamond exports in March 2001. The Special Court for Sierra Leone convicted Taylor in 2012 and sentenced him to 50 years in prison.

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8. 17.05 · Ethics

   G7 and EU bans on Russian diamonds

   Russia’s state-controlled Alrosa is the world’s largest diamond miner by volume. After Russia invaded Ukraine, the United States banned imports of Russian non-industrial diamonds in March 2022 (Executive Order 14068) and designated Alrosa in April 2022 (Executive Order 14024). G7 leaders agreed on December 6, 2023 to restrict Russian diamonds, and the EU’s 12th sanctions package of December 18 set the timetable. Diamonds mined, processed or exported from Russia were banned from January 1, 2024. Russian diamonds cut in third countries were banned from March 1, 2024 at 1.0 ct and above, and from September 1, 2024 at 0.5 ct and above. The US applied the same thresholds.

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Print the care chart for all 25 stones →A4 · PDF · 133 kBUS Letter · PDF · 132 kB