Spathic Calcite and Marble in the Wall-Paintings of Roman Aquileia

Marble and spathic calcite (or sparry calcite) are two forms of highly crystalline calcium carbonates (CaCO3) hav- ing a different geological genesis. As referred by Vitruvius, they were employed as aggregates in mortars constituting the tectorium of Roman wall-paintings. In the making of the intonaco, the Roman author empirically distinguished these two minerals: he suggests to use marble chips discarded from marmorarii only if salis micas (bright grains) ex- tracted from carbonate rock veins (spathic calcite) are not available (V . 7. 6, 1). In fact, several researches proved that, in the intonaco of Roman wall-paintings, spathic calcite aggregates are always prevailing on marble ones. In the wake of a research project promoted by the Department of Cultural Heritage and by the Department of Geosciences of the University of Padua, we fully analysed throughout a multi analytical approach more than sixty wall-painting samples from Aquileia (Friuli Venezia Giulia, Italy), having different chronologies spanning from the late 2nd c. BC to the 5th c. AD. In the present paper, we discuss the use of spathic calcite and marble in the tectorium of wall-paintings of the ancient town, providing information about their circulation in Aquileia along time