Magnetic Properties of Yamato-7301(j), -7305(k) and -7304(m) Chondrites in Comparison with Their Mineralogical and Chemical Compositions

Magnetic properties, represented by the magnetic hysteresis curves at room temperature and the thermomagnetic curves, of Yamato-7301 (j), -7305 (k), and -7304 (m) chondrites are compared with their chemical and petrographic compositions. Yamato (j) chondrite (H4) contains a metallic phase of 8.0wt% comprising kamacite of 5.3wt% Ni and smaller amounts of plessite and taenite, accompanied by non-magnetic metallic oxides. It seems very likely that the metallic oxides were in the form of hydroxides in the original state and were transformed to substituted magnetites by a heating. The metallic phase has been much oxidized by severe weathering. Yamato (k) chondrite (L5) contains a metallic phase of 8.6wt% comprising kamacite of 6.5wt% Ni and α_2-phase of (13-25)wt% Ni, suggesting that this chondrite was reheated to about 1000℃ and rapidly cooled to result in a production of α_2-phase. Yamato (m) chondrite (L5) contains a metallic phase of 8.3wt% comprising kamacite of 5.5wt% Ni and taenite, suggesting that this chondrite was almost equilibrated because of its very slow cooling and no appreciable effect of later metamorphism. Tables 3 and 4 give their basic magnetic properties, and Table 2 their chemical compositions.