Mineralogical and petrographical characteristics of white Apuan Marbles

This study contributes to the knowledge of the compositional, mineralogical, microstructural and physical characteristics of the Apuan marbles, focusing the attention on the existing relationships among these different parameters. For this purpose samples of marble, primarily white, coming from different zones of the Apuan Metamorphic Complex, were investigated. The studied samples show homogeneous chemical-mineralogical composition. They are characterised by high CaO content, low SiO2, Al2O3, MgO and Fe2O3 amounts. On the other hand, it is clear that the microstructural characteristics vary not only among different basins (e.g., Carrara and Arni basins), but also within a same basin. This is the result of the complex tectono-metamorphic history suffered by the Apuan marble. Samples characterised by grain boundaries from straights to slightly lobates without shape orientation, up to terms characterised by strong orientation and grain boundaries from interlobates to strongly sutured were analysed. Microstructural parameters were measured through image analysis methods in order to quantify the mean grain size and its distribution and to evaluate the presence of crystals shape orientation and the grain boundaries convolution. The different microstructural characteristics were connected with the main physical characteristics of the stone material: total open porosity, mesoporosity, pore size distribution, imbibition coefficients, saturation indexes, trends of saturation curves obtained from total immersion and capillarity. It's evident that the microstructural characteristics strongly influence the petrophysical parameters of the examined white marbles.