Beschreibung:
<jats:title>Abstract</jats:title><jats:p><jats:italic>Breccia verde di Sparta</jats:italic> is the traditional name given by the Roman marmorarii of the 19th century to a brecciated volcanic rock whose unknown precise provenance has been determined here for the first time through exploration of the broader area of Psefí (south of Krokees, province of Sparta, Peloponnese, Greece). This location was well known in antiquity and in modern times for having been exploited by the Romans for an important green porphyry named <jats:italic>lapis lacedaemonius</jats:italic>, nowadays also known as <jats:italic>porfido verde antico</jats:italic>. This breccia has been seldom used in Roman times for <jats:italic>opera sectilia</jats:italic>; in contrast, it appears more frequently reused in medieval floors; it is also frequently present in historical lithotecs formed in the 19th and 20th centuries. To fully characterise it and determine its relationships with green porphyry, <jats:italic>breccia verde di Sparta</jats:italic> samples from the newly discovered source have been thoroughly studied minero‐petrographically and geochemically, and their complex genesis has been reconstructed. It appears that after extrusion the original brecciated basaltic andesite underwent extensive hydrothermal low‐grade metamorphism, with a complete alteration of the igneous assemblage and minerals that preserved only part of the clinopyroxene phenocrysts. Alteration was accompanied by crystallisation of abundant epidote and chlorite, which imparted its predominant green colour to the rock. These breccias intruded in the lithoclases of the porphyry.</jats:p>