Synchrotron X-ray computed microtomography: studies on vesiculated basaltic rocks

Synchrotron X-ray computed microtomography (CMT) was applied to five basalt samples from different locations in order to determine the microgeometrica l structures and physical properties of vesicles. Two vesiculated basaltic lavas and one calcite-filled vesiculated basaltic lava were collected from the Lesotho Highland, South Africa, and two basaltic scoria tephra were tak en from the Lungkuan Volcano Group in northeast China. They were examined w ith CMT on the X27C beam line of the Brookhaven National Synchrotron Light Source. The voxel size varied from 10 to 20 mum depending on the chosen fie ld of view of the tomographic instrument. A fast-filtered back-transform (F FBT) algorithm was employed in the tomographic reconstruction. A 3D image g eometry analysis package was used to measure the vesicularity, specific sur face area and interconnectivity of the vesicles. The results of the analyse s showed that the bubbles have roughly spheroidal forms of different sizes. Vesicularity ranged from 45% for lavas to 80% for scoria. At least 90% of the vesicles are interconnected. Specific surface area was determined both by counting voxel faces and by use of two-point correlation functions.