[meteorite-list] Re: Weird bit-o-space The Rules of Chondrule colors

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Wed Oct 25 00:38:53 2006
Message-ID: <20061025043840.16329.qmail_at_web51005.mail.yahoo.com>

As to identifying minerals through photographs let me
mention... this is why God created thin sections and
polarizing microscopes....and as man came to better
understanding the micro probe was given unto him(Grin)

There are no CAI's that I see in this specimen.
Someone has some great CAI photos from Allende once
posted to the list.

As a rule of thumb: (statistically speaking):
Light colored chondrules with be feldspatic aka
feldspars. The "potassium sodium calcium aluminum
silicates"(tectosilicates). Examples Orthoclase
(KAlSi3O8), e.g Albite (NaAlSi3O8) and Anorthite
(CaAl2Si2O8. Terrestrial felspars come in
paractically all colors especially white,cream,
pink,green as in microcline, blue and with shilleren
as in Labadorite.

Black probably amphibole.

(Dark--less than black/bronze/gray/deep brown are
pyroxene or olivine aka Magnesium Iron Silicates
who's silicon bonding varies based on the amount of
oxygen in the source mix. If there is sufficient
oxygen the silicate tends to for a tetrahedron of 4
oxygens and one silicon. Olivine is a nesosilicate
where single tetrahedrons orient in one of 2-3
preferred patterns.

Pyroxenes and amphiboles are the inosilicates; single
chain silicates (pyroxenes) and double chain silicates
available)link in long molecules to satisfy the
shortage of oxygen. These form when oxygen is in a
lesser proportion and the molecules have to double up
on the bonds. (e.g enstatie, augite,
aegirine,bronzite).

Caution: Metallic Iron and Troilte can look gray or
bronze.

(For perspective Mica is a phylosilicate or sheet
silicate which bonds only in two planes ergo it is
easily peeled off in sheets)

As per the map #5 and possibly #6 look like
pyroxenes/olivine #5 being a barred chondrule.
Northwest of #5 is an interesting non spherical
chondrule-looking critter.

#4 could be one of the cryptocrystilline( fiberous
pyroxine/amphibole chondrules described in the
Wikipedia article below.
<http://en.wikipedia.org/wiki/Chondrule>
There are also pyroxinoids( inosilicate-like minerals
with calcium or phosphorous,etc) which distort
"normal" crystal growth which tend to kink and fold
back on themselves.

A description of silicate lattices for the diehards:
<http://ccp14.minerals.csiro.au/ccp/web-mirrors/xtaldraw/crystal/silicate.htm>

One suggestion for future some scale item in the photo
for reference. Good map work otherwise.

Elton
Received on Wed 25 Oct 2006 12:38:40 AM PDT