[meteorite-list] a question on fusion crust

[Armando Afonso]

Obviously, it is a diferent material...
The external fusion crust of iron meteorites is Magnetite, the result of the
combination with the air`s oxygene.
AA

----- Original Message ----- 
From: "Michael Farmer" <meteoriteguy at yahoo.com>
To: "Mr EMan" <mstreman53 at yahoo.com>; "Michael Murray" 
<mmurray at montrose.net>; <Meteorite-list at meteoritecentral.com>
Sent: Thursday, March 22, 2007 4:14 PM
Subject: Re: [meteorite-list] a question on fusion crust



> This is simple.

>

> Fusion, the result of material burning at extreme

> temeratures, and crust, the layer on the surface that

> was not there before re-entry.

> Thus, FUSION CRUST

> It is quite obvious that the surface of a freshly

> fallen iron, with the blue-black coating is a FUSION

> CRUST.

> It generally can't be "wiped" off. I have pieces in my

> collection, Bugoslava for example, with a .5 mm layer

> of blue-black fusion crust, that survived cutting and

> polishing of the meteorite, so it is not exacly

> "soot". Of course the crust is the same as the parent

> material, even on stones. How could it be of a

> different material? How could an object, falling

> through the atmosphere, get coated with anything but

> it's own matrix as it burns? Yes, the silicates can be

> altered due to heating, while irons tend not to

> chemically alter.

> Elton, I think you are about the only one in the world

> that thinks fresh fallen iron meteorites do not have

> fusion crust.

> Michael Farmer

>

> --- Mr EMan <mstreman53 at yahoo.com> wrote:

>

>> The "soot" coating you are talking about is mostly

>> freshly created magnetite (micro /nano crystals)

>> from

>> the oxidation of iron whilst passing through the

>> incandescent phase.  It adheres by magnetism and can

>> be wiped off with rough handling.  There is probably

>> a

>> carbon component however graphite turns to carbon

>> dioxide upon burning   >

>> There are several other terms for the zone

>> associated

>> with "ablation" heating, one of which is in the

>> literature: "zone of thermal alteration". When there

>> is  an oxidation coat

> .

> native elements such as

>> found

>> on sodium or phosphorus it is sometimes called a

>> rind.

>> This is what I favor to describe the coatings on

>> irons--the one before terrestrial oxidation also

>> known

>> as rust.

>>

>> In my view there can be no crust when the chemical

>> and

>> physical characteristics of the surface do not

>> differ

>> from the donor material.  That lets the door open

>> for

>> irons having crust and at least most agree that it

>> is

>> unlike the fusion crust of stoney meteorites.

>>

>> While at the Smithsonian inspecting the collection

>> up

>> close and personally, I was advised to use caution

>> in

>> examining a fresh iron as the coating would rub off

>> easily. They didn't call it fusion crust but the

>> issue

>> never came up. The point being, not everyone is in

>> agreement nor is there universal usage.

>>

>> Critical analysis on the assumptions about fusion

>> crust on irons would likely lead to a more

>> descriptive

>> table of composition and relate that to the

>> metallurgy

>> and chemical composition of the meteorite itself. In

>> fact I believe research on crustal petrology would

>> be

>> reveling for all types of meteorites. I yet wonder

>> why

>> some lunarites have a brown bubbly crust. The crust

>> of

>> a iron meteorite on Mars will be different from one

>> here and I'd like to know what to expect and why.

>>

>> Intuitively, I know there would be rare minerals

>> such

>> as nickel oxides,nitrates, phosphates  perhaps even

>> a

>> sulphide and yes even O3 and O4 silicates.  However

>> current wisdom is that crust is crust ego no

>> research

>> needs to be contemplated-NOT.

>>

>> Some of the oft quoted god status experts who write

>> of

>> fusion crust on irons monitor this list and have

>> remained curiously silent on the topic. I hope this

>> topic is thought provoking for all parties.

>>

>> I suppose that the use of the term "fusion crust"

>> universally with respect to irons is acceptable if

>> one

>> doesn't have a need for technical accuracy. One

>> thing

>> yet to be refuted here on the list is that the

>> "crust"

>> on irons is not composed of "glass".

>>

>> Elton

>>

>> --- Michael Murray <mmurray at montrose.net> wrote:

>>

>> > Hi List,

>> > Are you ready for a dumb question!  Here goes...

>> Is

>> > there a more  definitive description of the

>> blackened outer layer on the surface of iron

>> meteorites than simply referring to it as "fusion

>> crust"?  From what I can gather looking at different

>> pictures of stonys, they seem  to have a glassy or

>> melted layer of the material of the stone.  I can

>> see

>> that being a 'crust'.  On at least some irons, there

>> is a coating   but it doesn't appear glassy, just

>> blackened.   I'm guessing that  that coating is

>> partially resulting from burning of the gases in the

>> atmosphere?  If it is a 'crust', it is not much of

>> one.  It looks

>> like a very thin coating of soot that is adhered to

>> the stone,  although more durable than soot.  This

>> is

>> probably one of those dumb questions that the

>> Collection of Wisdom would answer.

>>

>>  The stone in this picture has the blackened layer

>>  I'm referring to:

>>

> <http://i127.photobucket.com/albums/p124/mmurray_02/IMG_0319.jpg>

>>  Michael Murray

>> ______________________________________________

>> Meteorite-list mailing list

>> Meteorite-list at meteoritecentral.com

>>

> http://six.pairlist.net/mailman/listinfo/meteorite-list

>>

>

> ______________________________________________

> Meteorite-list mailing list

> Meteorite-list at meteoritecentral.com

> http://six.pairlist.net/mailman/listinfo/meteorite-list