[meteorite-list] Lunar question

[Randy Korotev]

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