Pietra Di Santa Brigida Combed, Brushed, Honed Surface Finishes

The sandstone outcrops in the St. Brigid and that is cultivated in the homonymous cave is part of the geological formation of sandstone of Monte Senario, tentatively attributed to the Oligocene. It is a filiscioide training that can be considered a facies eteropica, westernmost, of Boulder (the formation from which the classic Florentine Pietra Serena) whose sandstone rock types have therefore compositional characteristics, structural and macroscopic closely related to the latter.
E 'consists of predominantly sandstone torbidiche, clearly graded, from medium to coarse grained, interspersed with argillaceous beds. The composition is quartz-feldspar-mica and the "cement" that binds the clastic grains is clay and calcite; the association is made up of clay minerals: chlorite, chlorite-vermiculite, illite and kaolinite, just like in Pietra Serena. From the petrographic point of view, quest'arenaria is classified as a feldspathic greywacke with provenance of clastic material mainly from acid magmatic intrusive rocks and subject of metamorphic and sedimentary rocks.