A mechanism for the formation of well rounded fragments created in pipes of Kimberlite - volatile-rich magmas from the Earth’s mantle that give rise to diamonds - is reported in a study published in Nature Communications this week. The work may give insight into dynamics of volcanic eruptions.

Kimberlites are a source of diamonds and are therefore of economic importance. The pipes formed by the kimberlite magma, which contain the pelletal lapilli particles, are also the locus of high-intensity explosive eruptions. Thomas Gernon and colleagues studied two of the world’s largest diamond mines in South Africa and Lesotho and propose that pelletal lapilli are formed when fluid kimberlite magma intrudes into earlier volcaniclastic infill close to a pipe root. They suggest that a similar origin may apply to pelletal lapilli in other volcanic rocks.