GTW1 is a mortar from the Gubbio Town Walls, Section Cassero.
It is a mortar consisting of about 50% in volume of aggregate with a grain size in the field of average to very coarse sand (0.2-2.3 mm). The picture below on the right shows the diffraction spectrography of GTW1.
Moderate to scarce sorting.
Roundness variable from angular to sub-rounded Low sphericity.
Without preferred orientation of the grains (see left picture below).
The aggregate is composed of lithic fragments (biomicritic limestones, cherts, arenites and rare metamorphic rocks) and monocrystalline grains (sparry calcite, quartz, plagioclase, K-feldspar, white mica and biotite, often chloritized, iron oxides and hydroxides) and diffuse calcium carbonate remains of organisms (mostly planktonic foraminiera).
The micritic lime binder is nearly homogeneous but highly porous (porosity 20-30 %vol) due to voids of irregular shape and cracks. The high porosity make difficult the evaluation of the original binder/aggregate ratio.
