Dear CMS Members: The 10th biennial Reynolds Cup (2020) competition for quantitative mineral analysis is now open. The competition is open to anyone interested in quantitative mineral analysis, with particular emphasis on clay mineralogy. Information about the competition including how to register, guidelines, key recommendations and previous winners can be found at http://clays.org/Reynolds.html We look forward to your participation! Sincerely, Steve Hillier, Helen Pendlowski, Ian Phillips Reynolds Cup 10 (2020) organizers