[meteorite-list] Question about nickel [nickel-poor iron meteorites]

From: Rodrigo Martinez <benig_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:06 2004
Message-ID: <000901c227c8$7aeba040$331807c8_at_oemcomputer>

Hola Piper and list
Piper, Thank you for the information about nickel, this is very complete
and well reference.
I tell you news about the Bellsbank group ( Bellsbank, La Primitiva,
Tombigbee River and Twannberg ) now these formed a new iron group
IIG due to a new discovery in the Atacama Desert. This new meteorite called
Guanaco is the fifth member of this group and was analyzed by John
Wasson (UCLA). This information is in www.meteorites.cl/science.html
Thank you.

Best Regards

Rodrigo Martinez
Atacama Desert Meteorites
benig_at_entelchile.net
http://www.meteorites.cl
----- Original Message -----
From: "Piper R.W. Hollier" <piper_at_xs4all.nl>
To: <meteorite-list_at_meteoritecentral.com>; "Rodrigo Martinez"
<benig_at_entelchile.net>
Sent: Tuesday, July 09, 2002 5:19 AM
Subject: Re: [meteorite-list] Question about nickel [nickel-poor iron
meteorites]


> Hello Rodrigo and list,
>
> Vagn Buchwald's "Handbook of Iron Meteorites" (1976) has a rather detailed
> discussion of nickel content on pages 76-77 with several histograms
showing
> the frequency distribution of percentage nickel content. He states, "In
> iron meteorites, nickel varies from a minimum of 5.1-5.3% (Tombigbee
River,
> Auburn, Holland's Store) to a maximum of 35% (Santa Catharina). If
> Oktibbeha County, page 947, is confirmed as an independent meteorite, the
> nickel maximum increases to about 60%."
>
> In Buchwald's histograms, the most nickel-poor iron group, the IIA
> hexahedrites, show a bell-shaped distribution which drops off very sharply
> below 5.3%. Of course, Buchwald's data set is now 26 years old and
> meteoritic science has not stood still in the years since his masterpiece
> was published. Still, the only irons which I am aware of with nickel
> content below the 5.1% lower bound which Buchwald claims are the so-called
> Bellsbank trio, which includes Bellsbank, La Primitiva, and Tombigbee
> River. These are classified as chemically and structurally anomalous
(UNGR)
> but appear to be related to the IIAB irons. A nickel content of 4.3% was
> determined for Tombigbee River in 1973, a fact which Buchwald was
> apparently unaware of at the time his Handbook was published. A paper
> published in 1984 by Malvin, Zong, and Wasson presents a hypothesis for a
> process which may have allowed the Bellsbank trio to form under very
> exceptional circumstances in isolated pockets of phosphorus-rich melt in
> the IIAB core, with their anomalous composition as a result. This paper is
> available online at http://adsabs.harvard.edu/abstract_service.html
(search
> for "Bellsbank").
>
> All things considered, it seems much more likely that an iron specimen
with
> nickel content below around 4% is manmade rather than a representative of
> an as yet undiscovered group of iron meteorites. Buchwald points out that
> nickel is extremely siderophile ("iron loving"), even more so than iron
> itself. Processes of fractionation in the metal phase allow for a rather
> wide range of iron/nickel ratios, but the laws of physical chemistry seem
> to draw the line at around 4% as a lower bound.
>
> Best wishes to all,
>
> Piper
>
> Standard disclaimer: I am not now and have never been a professional
> meteoriticist or geochemist, and any personal opinions not supported by
> references to authorities more qualified than myself should be taken with
> the usual grain of salt.
>
>
>
Received on Wed 10 Jul 2002 12:13:49 AM PDT