73255 (281) Aphanitic Impact-Melt Breccia
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Fact sheet
Description: 

73255 is essentially an agglomeritic bomb with a clast-rich, non-vesicular core surrounded by a rind (up to 1 cm thick) of vesicular breccia that generally has a sharp contact with the interior core. The core is itself an agglomeration of melt breccias with numerous distinct clasts of various rock types. 73255 is a fragment-laden, impact-melt rock containing a high percentage of relict rock clasts; including clasts of gabbronorite, pyroxene anorthosite, mare basalt, felsite and aphanitic microbreccia. One gabbronorite clast contains 53% plagioclase feldspar, 40% orthopyroxene, 5% augite and ~0.5% ilmenite. Minor mineral phases include apatite, whitlockite, stanfieldite (Ca-Mg-rich phosphate), chromite, troilite, metallic iron, armalcolite and rutile. Minute grains of K-feldspar and K-Si glass are also reported.

The sample weighed 394.1 grams before analysis and has been dated at 3.88±0.04 billion years (Ar/Ar).

Further details of this and other Apollo samples are here: http://curator.jsc.nasa.gov/lunar/

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Not known
Ma = Millions of years ago
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metamorphic
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