kimberlite

Kimberlite is an ultramafic, volatile-rich igneous rock best known as the primary host rock for many diamond deposits. It forms deep in the mantle and ascends rapidly through the crust as steep, pipe-like intrusions called diatremes, delivering mantle material to the surface in explosive eruptions.

Mineralogy and texture vary, but kimberlite is typically greenish to brown and contains minerals such as olivine, pyroxene, and phlogopite, often in a brecciated, glassy groundmass. It is notable for mantle-derived xenoliths and, in economically important rocks, microdiamonds. Kimberlite magmas are rich in volatiles including carbon dioxide and water, and they carry a distinctive suite of trace minerals.

Diamonds form at depths of roughly 140 to 190 kilometers under high-pressure conditions and are brought to the surface by kimberlite magmas, which may or may not retain diamonds after eruption. Consequently, not all kimberlites contain diamonds, and diamond grade varies widely among pipes.

Geologic setting and age: Kimberlites are commonly associated with stable continental cratons and are known from a wide age range, from Archean to Phanerozoic, with many late-Proterozoic to Cenozoic examples. Their formation involves deep mantle sources and rapid ascent to surface, which helps preserve mantle-derived materials in the rock.

Distribution and economic significance: Kimberlites occur on several continents, including Africa, Russia, Canada, and Australia, and are the principal targets in diamond exploration. Mining focuses on pipes with demonstrated diamond content, though exploration also relies on indicator minerals and geophysical surveys.