abstract:Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice. In nature, it forms when meteorites containing graphite strike the Earth.
Dr. Kennett and colleagues have published evidence in the prestigious Proceedings of the National Academy of Sciences that a "black mat" from the sediment of a Mexican lake dates to 12, 900 years ago and shows a sudden peak of magnetic and carbon spherules, "nanodiamonds" of a kind known as lonsdaleite, and charcoal: all of it evidence of extreme heat.