[meteorite-list] Lunar question

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Sun, 06 Sep 2009 00:07:24 -0500
Message-ID: <ljg6a55qm8qi863k55hbk4i4pu03ovha6m_at_4ax.com>

On Fri, 04 Sep 2009 13:10:29 -0500, you wrote:

>With regard to the breccias, here are some things to look for:
>
>Aspect ratios of clasts in lunar breccias are practically never
>greater than 3 to 1.
>
>There is practically no preferred orientation of clasts in a lunar
>(or asteroidal) breccia. Preferred orientation requires gravity (or
>flow, which might happen in an impact-melt breccia, but is rare).
>
>Clasts are mostly angular, with only a bit of rounding on some. All
>rounding is caused by impact abrasion, which isn't nearly as
>efficient as rocks being tumbled by moving water.
>
>Clasts don't have rims and cores of any kind, except maybe from
>terrestrial weathering processes.
>
>If a clast is layered, it's not from the Moon. Layered rocks require
>gravity and air or water.
>
>Lunar breccias are remarkably uncolorful - just shades of
>gray. Nearly all the lunar meteorites from Oman are stained by
>hematite, however, causing reddish regions. The NWA stones
>(interior) are less colorful.
>
>Clast in lunar breccias never have geometric shapes like prisms,
>rectangles, etc.
>
>Most brecciated lunar meteorites are regolith breccias. These often
>have white clasts of anorthosite in a dark matrix of lithified
>soil. Impact melt and granulitic breccias are rarer and are
>remarkably unremarkable (sawn surface).

Randy, far be it from me to put words in your fingers, but I recall in an
earlier (a year or two ago) post from you on lunar regolith breccias, you
mentioned that in a lunar breccia, the clasts are more or less randomly sized,
while in most terrestrial breccias, the clasts are mostly of similar sizes
because of wind, water, or gravity sorting them. (Correct me if I'm wrong with
this addition to your list.)
Received on Sun 06 Sep 2009 01:07:24 AM PDT