Stony-iron Meteorites: An Introduction

UCLA Meteorite Gallery Lecture Series - December 2021
Title: Stony-iron Meteorites: An Introduction
Lecturer: Dr. Alan Rubin; UCLA

There are two main kinds of stony-irons: pallasites and mesosiderites. Pallasites consist of roughly half metallic Fe-Ni and half magnesian olivine; these rocks were derived from the core-mantle boundaries of differentiated asteroids. Most pallasites belong to the main group (PMG) and are related to HED samples and IIIAB iron meteorites. Five pallasites belong to the Eagle Station (PES) group; these rocks are from differentiated carbonaceous-chondrite-like

asteroids. Their olivine grains are more ferroan than those of PMG (Fa20 vs. Fa12). There are also a few pyroxene pallasites that contain more pyroxene than PMG or PES and have distinct O-isotopic compositions.

Mesosiderites contain approximately half silicate and half metallic Fe-Ni, but the silicate in these rocks is mainly basaltic with relatively little olivine. Mesosiderites are impact breccias, probably formed by the collision of a largely molten metallic core with the basaltic crust of another differentiated asteroid. This occurred early in Solar-System history.

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