Large Type IIa Diamond from Arkansas, USA
The GIA lab in Carlsbad recently had the opportunity to examine a truly “all-American” diamond. The 1.16 ct near-colorless cushion-cut stone was submitted for a grading report along with a certificate from Crater of Diamonds State Park in Arkansas, USA, indicating it was cut from a 2.73 ct rough diamond mined in July 2020 by William Dempsey. The diamond was reported to have been cut and polished domestically in North Dakota (see above). It was ultimately graded as H color (near colorless) with SI1 clarity (due to an internal feather). Crater of Diamonds State Park is the only fee-dig diamond mine in the world where anyone with a prospector’s spirit can search in hopes of finding a true gem (Summer 2020 Gem News International, “Finders, keepers: Field trip to Crater of Diamonds, USA,” pp. 311–314). At 2.73 ct, the rough stone was exceptionally large for an Arkansas diamond, most of which come in significantly under 1 carat.
Researchers at GIA were excited to study this unique stone, especially with the prospect of analyzing inclusions that might shed light on the geological history of the Arkansas diamond deposit. However, the diamond turned out to be fairly clean with no crystalline inclusions. Somewhat unexpectedly, FTIR spectroscopy revealed the stone to be a type IIa diamond with no measurable nitrogen impurities. Type IIa diamonds are extremely rare among natural diamonds, and some have even been shown to grow much deeper in the earth than most type I diamonds (E.M. Smith et al., “Large gem diamonds from metallic liquid in Earth’s deep mantle,” Science, Vol. 354, No. 6318, pp. 1403–1405). The lack of inclusions in the stone was consistent with its type IIa character. Imaging with the DiamondView instrument showed relatively even blue fluorescence. Photoluminescence spectroscopy confirmed the natural origin of the diamond.
Discovering a type IIa gem diamond is remarkable enough, but uncovering one from a source in the United States, where few diamonds occur, is definitely a noteworthy event.
