Reflectance spectroscopy and mineralogy of primitive achondriteslodranites

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Reflectance spectra of three mineralogically characterized primitive achondrites have been measured for the first time and are compared with that of 29 Amphitrite to gain better understanding of the origin of the S-type asteroids. Those achondrites can be arranged in order of increasing degree of reduction from chondrites as follows : Acapulco-type winonaites Allan Hills (ALH)-78230 and ALH-77081,lodranite Yamato (Y)-791491,and a partly reduced lodranite Y-74357. A proposed pairing of Y-791491 with Y-791493 has been supported by our mineralogical characterization. Olivine crystals in Y-74357,which is similar to carbon-free ureilite, have many fractures decorated by troilite, and Mg/(Fe+Mg) ratio more reduced than that of the coexisting pyroxene. As a result of simulations of the reflectance spectrum of Amphitrite by those of the primitive achondrites and an iron meteorite, we suggest that a primitive achondrite more reduced than Y-74357 can reproduce the S-type spectrum.
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