Pelletal Lapilli (IMAGE) University of Southampton Caption Kimberlite volcanoes, the primary source of diamonds, contain pelletal lapilli -- enigmatic magma-coated clasts. These are generated deep in the volcanic vent by a granulation process analogous to that commonly used in coating chocolates, drugs and fertilizers. Credit University of Southampton Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.