Monomineralic Aggregates in Mortars: Examples From Lombardy (Northern Italy)

Abstract

Scientific analyses were carried out on mortar samples sourced from heritage buildings of Lombardy dating from fifteenth to nineteenth century (Milan, Como, Mantua etc.). The methods employed were optical microscopy on thin section and X-ray diffraction on powder. The mortars in Lombardy were generally made of lime or gypsum (binder) and sand, rock or brick fragments (aggregate), but an interesting character, especially marking the stuccoes, is the use of a monomineralic aggregate made of calcite or quartz grains. The calcite is present in two forms: subrounded polycrystalline and angular monocrystalline grains; these features are related to the crushing of marble (polycrystalline) or of calcite veins (monocrystalline). The quartz is also present in two forms: polycrystalline and monocrystalline grains with angular boundaries; in this case, the features are related to the crushing of metamorphic rock (gneiss).