Quantitative analysis of X-ray microtomography images of geomaterials: Application to volcanic rocks

X-ray computed microtomography is an excellent tool for the three-dimensional analysis of rock microstructure. Digital images are acquired, visualized, and processed to identify and measure several discrete features and constituents of rock samples, by means of mathematical algorithms and computational methods. In this paper, we present digital images of volcanic rocks collected with X-ray computed microtomography techniques and studied by means of a software library, called Pore3D, custom-implemented at the Elettra Synchrotron Light Laboratory of Trieste (Italy). Using the Pore3D software, we analyzed the fabrics and we quantified the characteristics of the main constituents (vesicles, crystals, and glassy matrix) of four different types of pyroclasts: frothy pumice, tube pumice, scoria, and "crystalline" scoria. We identified the distinctive features of these different types of volcanic rocks. The frothy pumices show vesicles that coalesce in isotropic aggregates, especially toward the sample interior, while the scoriae have a low porosity and an abundance of isolated vesicles. In the "crystalline" scoria sample most of the vesicle separation is due to the presence of crystals of different types, while the tube pumice shows an anisotropic distribution of vesicles and crystals at the microscale, as also observed at the scale of the hand sample. Quantitative analysis and textural information may supply an additional tool to investigate the eruptive processes and the origin of volcanic rocks.