Abstract
Rocks form in three dimensions through time and studying them gives us access to the interior of dynamic systems we can’t otherwise observe. Yet how we typically access the interior of rocks to gain that information may restrict insight, and influence how we reconstruct the processes that formed them. We demonstrate combined non-destructive 3D X-ray imaging techniques that produce quantitative densitometric and crystallographic maps of entire individual grains inside a rock. Olivine grains throughout a sample of the carbonaceous chondrite Northwest Africa (NWA) 11346 were each characterized by size, shape, composition, zoning intensity, and crystallographic orientation. The addition of 3D crystallographic mapping to calibrated 3D densitometric analysis—used to calculate composition—demonstrates a fully non-destructive petrographic method and provides unique insight. For instance, in our case, using crystallographic data to delineate individual grains and then measuring the 3D size, shape and composition of each distinguishes variably reset relict grains from those later crystalized after a melting event. Intersection in a 2D slice could not have led to this interpretation because the integration of three-dimensional size, rounding, composition, location and crystallographic orientation measured from each grain form the key patterns. Multimodal laboratory X-ray imaging has strong potential to advance 3D petrography.
