Feature Gems & Gemology, Fall 2003, Volume 39, No. 3

An Investigation into the Cause of Color in Natural Black Diamonds from Siberia

Black and dark gray diamonds from Siberia, Russia, were studied by analytical scanning and transmission electron microscopy. Their color is caused by the presence of dark inclusions. Unlike some previous reports on black diamonds in which the dark inclusions were primarily graphite, the Siberian samples with the most intense black color contained predominantly magnetite inclusions, while the dark gray diamonds most commonly contained inclusions of hematite and native iron. Moreover, the black diamonds studied exhibited anomalously high magnetic susceptibility, which may serve as one criterion for determining the natural origin of black color.