The Gemological Institute of America (GIA) has announced that their research team in Gaborone, Botswana — joined by Tom Moses, GIA Executive Vice President and Chief Research and Laboratory Officer, and Dr. Wuyi Wang, GIA Vice President of Research and Development — examined “the Motswedi,” a massive 2,488.32-carat rough diamond recovered last year at Lucara’s Karowe mine.
What makes this rough diamond so important is that it’s the world’s second-largest gem-quality rough diamond crystal ever found — and the largest still in existence.
“This is undoubtedly a diamond of great historical importance,” said Moses. “I have been fortunate to examine many significant, large and very rare diamonds, but I have never seen a gem-quality diamond of nearly this size.”
Discovered in August 2024, it weighed 2,492 carats at recovery and now tips the scale at 2,488.32 carats (≈1.10 pounds, or 0.5 kilograms). Its Setswana name, “Motswedi” — meaning “water spring” — was chosen through a national competition in Botswana. The stone ranks just behind the legendary 3,106-carat Cullinan diamond, unearthed in South Africa more than a century ago.
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“It is a Type IIa diamond of remarkable size with exceptional gemological qualities.” – GIA
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We know what you are thinking.
You are thinking, “If it’s a Type IIa, with little or no perceptible nitrogen, then why does it look brown?”
© GIA, photo by Wuyi Wang.
Motswedi’s Reality
When we hear that a large diamond is Type IIa — essentially nitrogen-free — we often picture a large, flawless, D-color diamond. But the Motswedi is far from that: it shows fractures, cleavages, iridescence, and, most notably, a distinct uneven brownish tint.
This coloration is most likely inherent, caused by plastic deformation of the crystal lattice. (With no mention of evidence of foreign material in the fractures, the brown bodycolor is best explained as dislocation-related.)
If cut, some areas could yield near-colorless grades. Still, its fate remains an open question: will it be polished into smaller gems, or preserved whole as the largest rough diamond crystal in the world?
Diamond Type — Simplified Definition
Diamonds are classified into “types” based on the presence of trace elements in their crystal structure.
- Type I: Contain measurable nitrogen — the most common impurity in diamond.
- Type II: Lacks measurable nitrogen, making them much rarer.
- Type IIa: No detectable nitrogen (and no boron). Chemically the purest, often colorless, but structural distortions in the crystal lattice can produce brown, pink, or purple hues.
- Type IIb: Contain boron, which can give a grey or blue color (like the Hope Diamond).
While Type IIa is often equated with large, flawless, D-color diamonds — like many we’ve seen at auction — Motswedi is a reminder that chemical purity doesn’t guarantee absence of color.
Presentation in its Best Light
Being a 2400+ carat rough gem quality diamond crystal is incredibly important. Because of the obvious fractures, and the uneven brownish tint, one could hope that there are several large areas of cuttable colorless diamond.
Iridescence
In case you were wondering about the iridescent colors you are seeing in some of these images, iridescence is a separate phenomenon, caused by thin-film interference resulting from a thin layer of air trapped within a crack along the diamond’s cleavage plane or fracture break, having nothing to do with inherent body color.
A Question of Weight
During their study, the GIA team also noted about 1.50 carats of small fragments that had separated during cleaning and handling by the mining company, explaining the slight weight difference from the stone’s recovery weight of 2,492-carats and its examination weight of 2,488.32-carats (approximately 3½ carats different). Importantly, the examination revealed that the Motswedi is composed of several large gem-quality “blocks” with minimal inclusions — remarkable for a diamond of this size.
GIA has the most comprehensive gemological research effort in the world. A global team of more than 60 scientists, researchers, and technical staff conducts in-depth research into the properties of diamonds, colored stones and pearls. This GIA-funded research underpins the Institute’s education programs and industry-leading laboratory services, supporting its mission to ensure public trust in gems and jewelry.
