Magnetic Properties of Yamato-73-04 and Yamato-73-07 Meteorites

Two Yamato meteorites collected in 1973 in Antarcica, Yamato-73-04 and Yamato-73-07, may be identified to an olivine-bronzite chondrite and a hypersthene achondrite respectively from their petrographic and chemical compositions. Magnetic analyses indicate that native irons in Yamato-73-04 chondrite comprise 2.6wt% of 7wt% Ni kamacite and 4.3wt% of 13wt% Ni kamacite, and that Yamato-73-07 achondrite contains 0.24wt% of Fe^0 with small amounts of Ni and Co and less than 0.02wt% of 60wt% Ni taenite or Fe_Cr_xO_4. The natural remanent magnetization, NRM, of Yamato-73-07 achondrite can be distinctly separated into the original NRM of the undisturbed interior of 6.3×10^ emu/gm in intensity and the secondary NRM of the surface skin fusion crust of about 0.5mm in thickness. The secondary NRM is attributable to the thermoremanent magnetization acquired in a magnetic field of 0.44 Oe-probably the geomagnetic field

Notes on Magnetic Properties of the Yamato Meteorites

The magnetic properties of four typical samples of the Yamato meteorites, which were collected near the Yamato Mountains in Antarctica in 1969,have been examined. These meteorites are (a) enstatite chondrite, (b) Ca-poor achondrite, (c) carbonaceous chondrite (C3), and (d) olivine-bronzite chondrite. The basic magnetic properties of these samples have been determined on the basis of the magnetic hysteresis curves at room temperature and the thermomagnetic curves in a strong magnetic field (H=5.53k. Oe), with additional data of the electron microprobe analysis. The main magnetic constituents in the Yamato meteorites thus evaluated are 3 wt % Ni kamacite and 25 wt % Ni kamacite in (a), almost pure metallic iron and probably maghemite in (b), magnetite in (c), and 6 wt % Ni kamacite and 50 wt % Ni taenite in (d). The natural remanent magnetization (NRM) and its AF-demagnetization characteristics also have been studied for these meteorites. The coercivity of NRM against the AF-demagnetization is in a good positive correlation with the cosmicray exposure age of these meteorites. This result seems to support the Butler-Cox hypothesis that the cosmic-ray exposure is capable of converting the soft isothermal remanent magnetization in meteorites to remanence with a higher coercive force