Thanks Dennis for the question and Randy for a clear summary.
Jerry Flaherty
--------------------------------------------------
From: "Randy Korotev" <[email protected]>
Sent: Friday, September 04, 2009 2:10 PM
To: <[email protected]>
Subject: Re: [meteorite-list] Lunar question
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
[email protected]
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