Estherville Meteorite, a Mesosiderite

Mesosiderite meteorites are stony irons with roughly 50-50 proportions of each. The iron is asteroidal core and the stone is the crust of a differentiated asteroid. Mantle material is rare. Several formation scenarios have been proposed and scientists continue to discuss the matter. Mesosiderites are classified by mineralogy and texture. Estherville is an A3/4. That is, plagioclase content of the stony portion is greater than 25% (volume) with much of the remainder calcium-poor pyroxene. The matrix is a highly recrystallized melt breccia.

Metal (gray) and troilite (bronze color) among silicate clasts and a recrystallized silicate matrix. Estherville Mesosiderite. Incident light. Field of view is 3 mm wide.

 

Flecks of metal appear to have been injected with other material into fractures in mineral grains. Estherville Mesosiderite. Incident light. Field of view is 3 mm wide.

 

The same view in incident and cross-polarized light.

 

In thin section the silicate portion of the Estherville Mesosiderite is generally transparent because of the extensive recrystallization. Transmitted light. Field of view is 3 mm wide.

 

Views of Estherville Mesosiderite thin section in cross-polarized light at different magnifications. Zoning appears in some mineral grains.

 

 

 

 

 

 

About the Author

John Kashuba
John is a natural history enthusiast living in Oregon.
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