[meteorite-list] More on green spots in stoneys

[Zelimir Gabelica]

Hi Bernd, Jeff, Rob, all,

Bernd, I would fairly agree with your conclusions regarding the green phase 
discovered by Rob.
Many silicate minerals that contain larger quantities of Mg sometimes 
indeed often do show greenish shades.

If we just consider the pyroxene group (quite likely represented in stone 
meteorites though pyroxenes are far from being the only silicate group in 
stoneys), Augite (Ca,Mg,Fe2+)2Si2O6, Aegirine-Augite (Ca,Na)(Mg, Fe2+, 
Fe3+)Si2O6, Enstatite or Clinoenstatite (both Mg2Si2O6) and especially 
diopside, (CaMgSi2O6) often show green-like colors, at least when from 
terrestrial origin.

There are 22 mineral species in the pyroxene group, some other of them also 
containing, among other, Mg2+ cations (e.g. Donpeacorite, Jervisite, 
Kanoite, Omphacite, Petedunite or...Pigeonite, this latter mineral being 
very often present in ordinary chondrites!)

Still considering the pyroxene family, an interesting pyroxene candidate 
that would readily involve green color would be Kosmochlor, thus NaCr3+Si2O6.

In this case, I'd expect a frank green color, that most of Cr3+ bearing 
salts (silicates) would exhibit (synthetic silicate chemistry).

The mineral, as found in various terrestrial deposits, is indeed said to 
exhibit a "pale green" or "emerald-green" color (Mindat).
Its name etymology is interesting ("Kosmos" = Cosmic origin, while "chlor" 
= "green" in Greek)

I don't know if this phase was ever found in stone meteorites but it was 
reported to occur in at least 3 irons: Toluca (where it was first 
discovered), Coahuila and Canon Diablo...

I can provide a pic showing green kosmochlor from Myanmar (Mindat), where 
it apparently forms solid solutions with Jadeite and Na-Cr amphiboles (see: 
Mevel & Kienast, Bull. Miner. 109 (1987), 617); more recent data can be 
found in: "Shi et al., Miner. Mag., 69 (2005), 1059".

Can someone from the List host some of my archive pics ?

Also inteersting is the fact that pale green Cr- and Na-rich diopside 
(kosmochlor-bearing diopside) was observed in anhydrous group I mantle 
xenoliths (dunite, wehrlite, harzburgite, clinopyroxenite) hosted by 
Pliocene-Quaternary hawaiite from the Ngatutura volcanic field of the North 
Island, New Zealand (Ikehata et al., Smithsonian/NASA Astrophysics Data 
System, Amer. Geophys. union, Fall 2004 meeting abstracts).

Natalyite, Na(V,Cr)Si2O6 is also a potentially interesting candidate (still 
contains Cr3+ ions that are partly isostructurally replaced by V3+ ions; it 
is "light green to yellow-green" (pic on request)

Finally, I have in my meteorite coll. archives 3 pics showing a few similar 
pale-green millimetric rounded inclusions (most probably not chondrules, 
although...who knows ?).
They were taken under high magnification in daylight by Roger Warin, our 
local pic expert and thin-section specialist (see web site: www.agab.be , 
click on "thin sections"). These green spots are from my 459 g full slice 
"Belle Plaine" (Kansas) (242x195x5 mm).

Would be nice if someone (Bernd or...?) is willing to host these 5 pics 
should someone wish to have a look Contact me off list.

Very interesting subject...

All my best to all, expecting many of you had weird fun in Tucson (pics 
expected...)

Zelimir




A 20:02 01/02/2009 +0000, vous avez écrit :
>Hello Rob and List,
>
>http://home.planet.nl/~rlenssen/green_spot_in_chondrite.jpg
>
>"Can anybody explain to me what I am seeing here?"
>
>This may be a magnesium-rich orthopyroxene crystal => hypersthene (Mg,Fe)SiO3
>
>What do others think?
>
>Best,
>
>Bernd
>
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Prof. Zelimir Gabelica
Université de Haute Alsace
ENSCMu, Lab. GSEC,
3, Rue A. Werner,
F-68093 Mulhouse Cedex, France
Tel: +33 (0)3 89 33 68 94
Fax: +33 (0)3 89 33 68 15