[meteorite-list] Crust Micrographs NWA 2371 Crystal Structure! Check it out!

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Fri, 23 Mar 2007 22:32:40 -0700 (PDT)
Message-ID: <573218.52331.qm_at_web51008.mail.re2.yahoo.com>

Taking time out during my "expedition" to the
Wetumpaka astrobleme...
--- STARSANDSCOPES at aol.com wrote:
"The heating/ cooling caused the crust to crystallize
like nothing I have seen before..."

Not picking on you Tom but I am using this as a segway
to speak to fusion crust again. One of the reasons I
am so passionate is that I am tired of seeing all
these weathered and rusty meteorites on Ebay described
as having "great fusion crust". I await the
photographs, your collection is truly awesome.

When you said crystalized, perhaps you meant
solidified A technical point but important in truly
understanding what fusion crust is and is not.

By definition, meteorite crust can't re-crystallize
but it may contain partially melted material.
Silicate melt which is what comes from Common
Chondrites is known as "glass" in the technical sense,
meaning it is an amorphous solid-- (i.e. lacking
crystal structure, e.g tektite, obsidian) This glass
lacked the conditions of time and temperature to allow
the molecules of like compounds to regroup in crystal
form. Given the right conditions molecules tend to
reform crystals. Notice how long it takes honey to
turn to sugar crystals at room temperature? Only here
it would take eons to recrystalize and the material
would long be weathered away before that.

While I have Internet connection let me also mention
that the word "fusion"does not refer to burning but
refers to the technical term for the change of state
from solid to liquid. Hence the technical term fusion
temperature--meaning the temperature at which a solid
melts. Hence the origin of the terms and definition
"fusion crust"


So what you are seeing, Tom, must have a different
explanation. Else everything we know about physics
has to be redefined.


Elton
Received on Sat 24 Mar 2007 01:32:40 AM PDT