The vertebrate fossil locality of La Roma 2, Spain (Upper Miocene, Late Vallesian, MN10) is characterised by a high abundance of mammalian coprolites, which provide direct clues to the diets and habitats of the organisms that produced them. X-ray diffraction analysis showed a sample of hyaena (cf. Lycyaena chaeretis) coprolites to be mostly composed of calcium phosphate. Ultrastructural SEM and TEM studies revealed three successive phases of preservation, including an initial phase of mineralisation that produced microspherulites within a very fine-grained cement. This indicates that most of the calcium phosphate present in the coprolites precipitated rapidly, which in turn facilitated the formation of negative moulds of faecal bacteria within the coprolite matrix.This research was funded by the Dirección General de Patrimonio Cultural, Gobierno de Aragón (projects 02/92, 332/2006, 184/2007, 230/2008, ud 230/08/2009, and 230/08/09/2010), the Departamento de Educación, Cultura y Deporte, the Dirección General de Investigación, Innovación y Desarrollo, Gobierno de Aragón (Research Group E-62, FOCONTUR) and the Spanish Ministry of Science and Innovation (Project CGL2009-13903, Project CGL2010-19825, Projects CGL2010-16004 and CTM2009-12838-CO4-O3). MDP is a contracted researcher with-in the “Juan de la Cierva” programme (Ministerio de Ciencia e Innovación, ref. JCI-2007-132-565) at the Fundación Conjunto Paleontológico de Teruel-Dinópolis.Peer reviewe