A New Type of Meteoritic Diamond in the Enstatite Chondrite Abee

Science  10 Apr 1992:
Vol. 256, Issue 5054, pp. 206-209
DOI: 10.1126/science.256.5054.206


Diamonds with δ13C values of –2 per mil and less than 50 parts per million (by mass) nitrogen have been isolated from the Abee enstatite chondrite by the same procedure used for concentrating Cδ, the putative interstellar diamond found ubiquitously in primitive meteorites and characterized by δ13C values of –32 to –38 per mil, nitrogen concentrations of 2,000 to 12,500 parts per million, and δ15N values of –340 per mil. Because the Abee diamonds have typical solar system isotopic compositions for carbon, nitrogen, and xenon, they are presumably nebular in origin rather than presolar. Their discovery in an unshocked meteorite eliminates the possibility of origins normally invoked to account for diamonds in ureilites and iron meteorites and suggests a low-pressure synthesis. The diamond crystals are ∼100 nanometers in size, are of an unusual lath shape, and represent ∼100 parts per million of Abee by mass.