73255 (281) Aphanitic Impact-Melt Breccia
We would like to thank the following for the use of this sample:
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/
Ma = Millions of years ago
Rock forming mineral:
- metallic iron,