Magnetic properties of polycrystalline diamonds

The remanent magnetism and bulk magnetic properties of polycrystalline diamonds have been investigated. The diamonds are of two distinct types, those occurring together with gem-grade diamonds in kimberlite pipes in S Africa, and carbonados, found in placer deposits notably in Brazil and the Central African Republic. Both types generally possess measurable remanent magnetization, the former stronger than the latter, and stability tests indicate the presence of primary and secondary components. Magnetite is the dominant carrier of NRM in the kimberlite diamonds, but the very small content of magnetic mineral in the carbonados makes identification of the carrier difficult. Possible contributors are tetrataenite, native iron and cohenite. Anomalous acquisition of isothermal remanence occurs in some carbonados, saturation being unachievable in applied fields in excess of 1 T. The ratio of saturation remanence to initial NRM is anomalously low in some of the kimberlite diamonds, and the possibility of magnetic contamination is investigated.