73215 (195) Aphanitic Impact Melt Breccia
Collection:
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Microscope
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Fact sheet

73215 (195) Aphanitic Impact Melt Breccia

73215 is a noteworthy polymict breccia in that it contains a collection of rock clasts with a range of petrologic types and ages. It is essentially a collection of rock clasts included in an aphanitic, banded matrix of mineral debris. The overall structure of 73215 is dominated by “flow banding” formed by differential flow and/or shear during and after aggregation and consolidation. Minute white lines that are traces of planes of fine-scale shear are visible in all types of matrix and schlieren derived from flattened clasts are oriented parallel to shear planes. Abundant small lithic and mineral fragments are set in a dark aphanitic groundmass with minute grain size. The grain size distribution appears seriate. Reflected light shows that the matrix has a fine wormy porosity. Rotations show some of the larger plagioclase feldspar clasts including a partially maskelynised one (rotation 2). A notable pink spinel clast appears at the top right of our thin section. Ilmenite, zircon, troilite and metallic iron are other minor constituents.

The sample weighed 1062 grams before analysis and has been dated many times with a range from 3.92 to 4.22 billion years for different clasts (Ar/Ar).

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

About this collection

Apollo 17, the final manned landing mission, had two objectives: to obtain samples of ancient rocks from the lunar highlands and to look for evidence of younger volcanic activity on the valley floor.

This small Collection contains material deriving from both periods, including igneous rocks around 4.3 billion years old from the lunar highlands as well as younger volcanic samples dating from about 3.6 billion years ago.

Apollo 17 was launched on 7 December 1972.

Sample details

Collection: Apollo 17
Type
metamorphic
Rock-forming mineral
pyroxene
plagioclase
feldspar
Accessory minerals
ilmenite
zircon
troilite
metallic iron
spinel
Category guide  
Category Guide
Title
Refers to any word or phrase that appears in the individual rock names. Names are generally descriptive; they allow users to search for broad terms like ‘granite’ as well as more specific names such as ‘breccia’. However, the adjacent descriptions of the specimens captures a wider range of general words and phrases and is a more powerful search tool.
Description
Refers to any word or phrase that appears anywhere in the descriptions of the specimens
Accessory minerals
Minerals that occur in very low abundance in a rock. They are usually not visible with the naked eye and contribute perhapssver, they often dominate the rare elements such as platinum group metals.
Rock-forming minerals
Minerals that make up the bulk of all rock samples and are also the ones used in rock classi?cation.
Timescale
Selecting one or more period, for example 'Jurassic'.
Theme
A term used to group together related samples that are not already gathered into a single Collection. For instance, there is a ‘SW England granites’ theme that includes such rock types as granite, hydrothermal breccia, skarn and vein samples.
Category
A general term used to label a rock sample. It is a useful way of grouping similar samples throughout a collection. Category names are often, but not exclusively, common rock names (e.g. granite, basalt, dolerite, gabbro, greisen, skarn, gneiss, amphibolite, limestone, sandstone).
Owner
The owner of the sample that appears in the collection. For example, NASA owns all the samples that appear in the Moon Rocks collection
We would like to thank the following for the use of this sample: