by Brendan (originally posted 25th May 2012)

Pelletal Lapilli with a diamond core (Source:

Today I came across an interesting headline – Chocolates and diamonds: Why volcanoes could be a girl’s best friend, seems like an unusual combination to me, so I investigated further. It turns a team from the UK, led by Thomas Gernon have been investigating the formation of pelettal lapilli, which are small pieces of rock surrounded by quenched juvenile magma, or in simple terms a piece of rock coated in lava. These are commonly found within kimberlites, which are the major source of diamonds, with this study focusing on kimberlites in South Africa and Lesotho.

Still, you are probably wondering how chocolate becomes involved? In some cases the rock at the core of pelletall lapilli is actually a small diamond and they tend to be found in locations where large diamonds are found, rather than small diamonds. Investigating the processes that could cause the coating led the team to talk to mechanical and chemical engineers, who made the link with the process of fluidised spray granulation. This technique is used in the confectionary industry to add a smooth coating to chocolates, such as M&Ms, Maltesers and Smarties; there we have the link to chocolate. This process involves a low viscosity fluid (magma) being ejected at high pressure into a bed of particles, these particles are then fluidised and simultaneously coated in the magma.

Aside from involved three really interesting topics: diamond, chocolate and volcanoes, this research also caught my eye due to its interdisciplinary nature, particular the collaboration with chemical engineers, as I spent five years studying to be one, but then saw the light and stayed in the earth sciences. However I do always enjoy the unexpected crossovers that occur and fall back on some my engineering skills occasionally, particular the solid grounding in thermodynamics that I received. So often it is the cross over between earth science and physics, biology and the broader climate sciences that get all the attention so it good to see something different.

If you are interested the full paper can be found at Nature Communications.