English to Spanish Tech/Engineering Geology Se trata de un informe petrográfico de descripción de muestras de roca

Hand specimen shows pale greenish-buff coloured, fine-grained felsic crystal-lapilli tuff (clearly defined small fragments up to ~1 cm tend to be slightly darker, more sericite altered and contain more cubic limonite casts after pyrite; quartz phenocrysts may be up to 4 mm across), cut by thin pale orange-brown fracture coatings that react strongly to cold dilute HCl. The rock is not magnetic, shows only trace reaction to cold dilute HCl in the body of the rock, and variable yellow stain for K-feldspar/white etch for plagioclase in the etched offcut, depending on position in clasts versus matrix.
Lo encontré como roca o mineral que rellena un molde natural y también como contramolde, pero no sé si hay una sola palabra que sea equivalente al significado de cast.