Determination of bulk density for small meteorite fragments via visible light 3-D laser imaging

Abstract

Bulk density is an important intrinsic property of meteorites, but the necessary bulk volume measurement is difficult to do in a truly nondestructive way. Archimedean methods involving the displacement of a 40-100μm beads "fluid" are commonly applied, but can encounter systematic errors. Herein, we report a visible light laser imaging technique for the nondestructive measurement of meteorite surface features, allowing for the subsequent assembly of 3-D volumetric models; the method is particularly applicable to small meteorite fragments and to fragile specimens. We have acquired laser image data for 24 fragments from 18 ordinary chondrites, carbonaceous chondrites, and achondrites, with masses ranging from 265.0 to 1.2g. Laser imaging bulk density is consistent between sister fragments of meteorites down to sizes of about 0.5cm3, an order of magnitude smaller than can be reliably measured with Archimedean beads techniques. Uncertainty is less than 2% for fragments >4cm3, and typically between 2 and 4% for small fragments <4cm3. For 10 fragments, 3-D laser imaging volumes are on average 1.3% smaller than those obtained with Archimedean beads. In a wider comparison using 21 meteorite fragments, 3-D laser imaging bulk densities are on average 2.14±2.36% greater than the corresponding Archimedean method literature values for these meteorites. Difficulties in the procedure of 3-D image alignment may lead to a slight overestimation of meteorite bulk density, and so laser imaging-based bulk densities are maximum estimates that can be viewed as being complementary to the minimum bulk density estimates obtained using Archimedean beads methods. © The Meteoritical Society, 2011.