[meteorite-list] What is or is not a chondrule?

From: MEM <mstreman53_at_meteoritecentral.com>
Date: Mon, 23 Nov 2009 05:19:39 -0800 (PST)
Message-ID: <252713.87085.qm_at_web55204.mail.re4.yahoo.com>

Walter your email is not "yahoo friendly" so here is the answer via the list.

Hello Walter, I don't know if you ever got an answer to your question but I had it marked for follow up.

Chondrules, while usually more spherical, can be ovoid or ellipsoid and occasionally doubled. Current theory on chondrule formation is that they form by a varied sequence athat always includes final series of flash melting of the surface which seals in the contents. This tends to round off the edges and give them their typical spheroidal shape.

When we see the chondrules as you describe--with lots of lines, those are usually "barred" olivine chondrules. Barred olivines probably went through several passages between super hot and not so hot zones in the nebula and represent successive growth and melt phases. Some chondrules are simple feldspar. Some are "rubble piles" of angular blocks/globs of mineral grains and dust which were flash melting sealed them into a chondrule yet retaining their angular crumbled edges sucked into a sphere mosaic style.

A clast is usually angular on at least one side--that is not round. It has a consistent composition and color. Sometimes clasts are large enough for eye identification that they came from an entirely different class of meteorite then the one they have been found in.

Keep in mind that the process of moving from a stage 3 to a 6 involves melting away of the chondrules and migration of their contents into the matrix while semi-plastic. These chondrules are not easy to discern even with a hand lens as their margins are in a stage of blending into the matrix due to heating.

Regards,
Elton
--- On Thu, 7/6/06, Walter L. Newton <newtonw2 at comcast.net> wrote:

> From: Walter L. Newton <newtonw2 at comcast.net>
> Subject: [meteorite-list] What's a chondrule-what's not a chondrule?
> To: meteorite-list at meteoritecentral.com
> Date: Thursday, July 6, 2006, 10:06 AM
> Hi list, a little technical
> question.
>
> I understand what a chondule is, but sometime, when looking
> at a slice of a meteorite, I am confused as to what they always look like.
>
> I have a polished slice of NWA 787 (same as NWA 869). I see
> light brown
> sphere's but I also see light brown ellipsoid (is that the
> word I'm looking for?) splotches. The same thing exists for some light grey patches.
>
> The there are light brown or light grey "lines," maybe
> 2-3mm long. Is that a clast or inclusion or what?
>
> In a slice of NWA 2859 (H4) I see a few round grey metal
> patches. I suspect that just so happens to be a round blob of iron, not a chondrule.
>
> Most of the time when I see a picture that points out
> chondrules, the illustration always points to round objects. Do I assume if it's not round, it's not a chondrule?
>
> Walter L. Newton
> Golden, Co
Received on Mon 23 Nov 2009 08:19:39 AM PST