Analysis of the vesicular structure of basalts

We present a high resolution study of the void space geometry of vesiculated basaltic bombs (porosities in the range 60-80%) from three dimensional digitized images obtained by synchrotron X-ray tomography. The void space is composed of vesicles, the solidified remnants of expanding gas bubbles. Coalescence between bubbles complicates the identification of individual vesicles. Under the assumption that coalescence between two bubbles results in a well defined waist configuration (or throat) between the two resulting vesicles, we present an algorithm to locate the waist-spanning “contact surface” which conceptually separates each pair of coalesced vesicles. With contact surfaces identified, individual vesicles are isolated and analysis of their geometry and connectivity can be investigated. We present results for the distributions of vesicle volume, contact surface area and vesicle coordination number (the number of neighbors with which a vesicle has coalesced). We find that distribution for contact surface area is log-normal; the distribution for coordination number is a power-law; and the distribution of vesicle volumes is at least bi-modal.