Mineral inclusions in four Arkansas diamonds: their nature and significance

Totally-enclosed inclusions recovered from four Arkansas diamonds by burning in air at 820" C are identified by XRD and Eoex analyses as: (l) enstatite, olivine, pyrrhotite + pentlandite, (2) eclogitic garnet, (3) enstatite + peridotitic garnet + chromite, olivine + pyrrhotite, pyrrhotite, pentlandite, pyrite + pyrrhotite, pentlandite * a nickel sulfide, (4) diamond, enstatite, magnetite. This is the first report of nickel sulfide in diamond. A review of inclusions found in Arkansas diamonds shows a similarity with those from world-wide localities, and indicates a global consistency in diamond-forming environments. opaque and transparent totally-enclosed inclusions were apparent under binocular microscope examination. The 0.45 ct. stone was colorless and of elongated rounded shape with a highly polished surface. Four inclusions were detected. The 0.50 ct. crystal was a colorless rounded tetrahexahedron with a cleavage plane on one side and contained transparent and opaque inclusions. The 0.62 ct. diamond was also colorless and of rounded tetrahexahedral form. Several relatively large flat opaque inclusions ("carbon spots") were observed. All the diamonds were free ofdetectable surface cleavage cracks.