[meteorite-list] Lunar question

From: Randy Korotev <korotev_at_meteoritecentral.com>
Date: Fri, 04 Sep 2009 13:10:29 -0500
Message-ID: <200909041810.n84IAIW20826_at_levee.wustl.edu>

Dennis:

I might be able to answer your question, but I need to understand the
question better.

Do you mean "breccia basalt" as opposed to just "breccia?" Most
lunar meteorites are breccias, but only a few of the breccias are
basaltic. Most basaltic lunar meteorites are not breccias; they're
unbrecciated basalts. Did you follow that?

In my opinion, in the absence of a fusion crust it's impossible to
identify a lunar meteorite "just by looking," and I've seen
practically all of them. I have bought or been sent about 4 alleged
lunar meteorites from experienced collectors and dealers in the past
5 years that turned out to be terrestrial rocks, eucrites, or
howardites. I've seen some lunar meteorites, most notably the
Kalahari stones, that don't look anything like a moon rock or a any
kind of meteorite.

Some, if not many, terrestrial basalts "look like" martian and lunar
basaltic meteorites. So far, none of the lunar or martian basaltic
meteorites are as vesicular as are many terrestrial basalts, but lack
of vesicles sure doesn't make it a planetary meteorite. A chemical
or mineralogical analysis is neede to distiguish among terrestrial,
martian, lunar, and asteroidal basalts.

They're are some kinds of terrestrial rocks that strongly resemble
lunar breccias. Several people have sent me ignimbrites (alias
ash-flow tuffs or, more generically, volcaniclastic rocks) that look
like lunar breccias. There are also types of sedimentary processes
on earth that can lead to impact-breccia look-alikes.

http://meteorites.wustl.edu/meteorwrongs/m118.htm
http://meteorites.wustl.edu/meteorwrongs/m151.htm
http://meteorites.wustl.edu/meteorwrongs/m156.htm
http://meteorites.wustl.edu/meteorwrongs/m159.htm
http://meteorites.wustl.edu/meteorwrongs/m195.htm
http://meteorites.wustl.edu/meteorwrongs/m200.htm
http://meteorites.wustl.edu/meteorwrongs/m216.htm
http://meteorites.wustl.edu/meteorwrongs/m219.htm
http://meteorites.wustl.edu/meteorwrongs/m225.htm
http://meteorites.wustl.edu/meteorwrongs/m235.htm
http://meteorites.wustl.edu/meteorwrongs/m237.htm see this one, especially
http://meteorites.wustl.edu/meteorwrongs/m260.htm
http://meteorites.wustl.edu/meteorwrongs/m279.htm

Some porphyritic basalts resemble lunar breccias to the untrained eye.

http://meteorites.wustl.edu/meteorwrongs/m086.htm
http://meteorites.wustl.edu/meteorwrongs/m129.htm
http://meteorites.wustl.edu/meteorwrongs/m259.htm

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).

Hope this helps.

Randy Korotev




At 10:38 04-09-09 Friday, you wrote:

>Good Morning All... I have a rather novice question: What is the identifying
>tag or indicator that differentiates a Lunar breccia basalt from a terrestrial
>breccia? I have cut and examined several that I have found, and not
>knowing the difference, made coasters out of them... I know you guys that
>run to Morocco to purchase them, from time to time, have a good idea without
>taking a lab with you....
> Thanks!
>Dennis Miller
>
>Sorry, nothing to give away, but bare with me.....
>Oh, I did give one of my non-lunar coasters to Haag.

Randy Korotev
Saint Louis, MO
korotev at wustl.edu
Received on Fri 04 Sep 2009 02:10:29 PM PDT