Physical properties of some unequilibrated Antarctic ordinary chondrites

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The intrinsic and bulk densities, porosity, thermal diffusivity, and ultrasonic-wave velocities (V_p and V_s) were measured for four unequilibrated ordinary chondrites (Y-74156,-74191,-74647 and -75097). Thermal diffusivity was also measured for five equilibrated ordinary chondrites (ALH-77288,-77294,-78103,-78251 and MET-78003). V_p and V_s measurements were made for three mutually perpendicular directions at room temperature and one atmosphere pressure. Thermal diffusivity was measured under vacuum conditions (below (10)^<-3> mmHg) in the temperature range of 100 to 500 K. V_p and V_s values are much smaller than those expected from their mineral compositions. The decrease in V_p and V_s is much greater than that estimated from the porosity value itself. It is suggested that many oblate pores, i.e. cracks, exist in the samples. Aspect ratio of cracks is estimated to be much smaller than 0.05. Such thin cracks are presumably produced by impact events, although we cannot observe any heavy shock induced features in thin sections. Velocity anisotropy between transmitting dircctions is observed in almost all samples. Thermal diffusivities are also much smaller than those expected from their mineral compositions. Existence of many cracks is also suggested from the thermal diffusivity-porosity relations. Relationship between the measured physical properties and the petrologic types was investigated. For H chondrites we can see a rough trend that porosity decreases with increase in petrologic type number. For L chondrites, however, we cannot see any clear correlation between the physical properties and the petrologic types.
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Physical properties of some unequilibrated Antarctic ordinary chondrites

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