Emery meteorite, Hanson County, South Dakota, USAi

Regional Level Types
Emery meteorite	Meteorite Fall Location
Hanson County	County
South Dakota	State
USA	Country

Stony-iron, Mesosiderite-A3
Find, 1962; 16.7 kg

A single mass was found in a field by a 12 yr. old boy and left in pile of farmyard stones for about 6 years. With ~50 wt% Fe-Ni metal, comparable silicate abundances (~40wt%/~60vol%), minor troilite, and a few subsidiary phases, the Emery mass was quickly recognized as a mesosiderite. As a polymict breccia, Emery hosts a variety of lithic and metal clasts as well as single crystals. The major silicates are mildly magnesian orthopyroxenes ('hypersthene') and variable Ca-rich plagioclase both as crystals and in matrix. Smaller amounts of olivine (Fa18-28), tridymite, and augite are also found. Fe-Ni metal is predominantly kamacite with minor taenite. Additional opaques include oxides and merrillite plus traces of graphite and schreibersite. Coronas on the olivine crystals indicate high temperature reactions between the olivine and the mesosideritic matrix. Discussions continue as to how the slow metallographic cooling rates calculated for mesosiderite Fe-Ni metal, Ar39/40 'ages' of putative impacts 3.6 billion years ago, and high resolution oxygen-isotope affinities between the mesosiderites and the (mostly) Vesta-derived HED meteorites can be explained and reconciled.

Emery and 2 other mesosiderites are classified as a Mesosiderite-A3 (subgroup A = high plagioclase abundance; petrologic type 3 = largely reequilibrated matrix). As of 2000, the largest portions of the Emery mass were held at the Max-Planck-Institute for Chemistry in Mainz (3.92 kg), at UCLA (1.3 kg), and at National Museum in Washington, DC (1 kg). A number of smaller pieces have been distributed elsewhere.

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References