Thermally induced fractures in olivines of stony meteorites

Shock effects in olivine and implications for Hugoniot data

“…The blocky fracturing found in sample 13 (15.9-GPa peak pressure) is distributed homogeneously, and fracture orientations are more or less parallel to the cleavage directions of olivine. The fractures are reminiscent of those described by Levi [1973Levi [ , 1976 and may have a thermal origin or, alternatively, may reflect massive brittle failure at the Hugoniot elastic limit. The fractures separate blocks which are slightly misoriented with respect to each other but which exhibit no undulatory extinction, implying essentially no plastic strain within these blocks.…”

“…These zones of localized deformation surround regions of relatively unbroken olivine, suggesting the occurrence of heterogeneous yielding under shock, perhaps similar to that discussed by Grady [1977]. At a smaller scale, however, the regions between these fractured zones contain numerous microcracks ( Figure 6b) which are oriented along cleavage planes [see Snee and Ahrens, 1975;Reimold and Stbffler, 1978;Levi, 1973Levi, , 1976. With increasing pressure these small fractures tend to lose their planarity and apparent crystallographic constraint, sometimes taking on a wavy (or flowlike) appearance ( Figure 6c).…”

Thermal Deformation and Fracturing in Olivine‐rich Samples

“…Fatigue is also able to generate microcracks, giving rise to the propagation of fracture. Low-temperature thermal fatigue combines the change of mechanical properties due to the temperature variation and the periodical stresses so that it is able to give rise to a number of plastic and clastic deformations, both in metals and in stones (Levi, 1969(Levi, , 1973(Levi, , 1975(Levi, , 1976. The observed effects increase, with increasing number of cycles, in the affected crystals, while they extend progressively to previously unaffected crystals.…”

“…Bipyramidal and prismatic cleavage appeared as new features, not existing in the original material. It is known that similar features may be found in meteorites, when a sufficient degree of metamorphism is present, and may be induced as a consequence of shock (Muller and Hornemann, 1969) or low-temperature thermal cycling (Levi, 1973(Levi, , 1976.…”