[MSA-talk] wire iron

Modreski, Peter pmodreski at usgs.gov
Mon Dec 4 19:43:10 EST 2017


I'm sure others will answer, but let me try giving mine.  I've never heard
of any wire habit native iron, and I suspect, it's not known.

I think that exactly how/why wire silver and gold form has always been a
puzzle and mostly remains so.  There is a very good article in the July/Aug
2017 issue of Rocks & Minerals about wire habit native gold and silver:

Connoisseur's Choice: Wire Silver, Kongsberg, Norway & Wire Gold, Ground
Hog Mine, Gilman, Colorado, by Calvin J. Anderson and John Rakovan (vol.
92, no. 4, pp. 344-357)
and, though the article is mostly descriptive, I think if the authors were
aware of any definitive evidence about how they form, they would have
referred to it.  As far as they get is quoting Anderson et al. (2017), to
say that "although silver wires might appear to be single crystals or
polycrystalline bundles of whisker-shaped crystals, they are actually
polycrystalline with striations “merely superimposed on an equigranular
grain texture” ".

One could make hypotheses about it, of course...

Pete Modreski

On Mon, Dec 4, 2017 at 3:52 PM, Magloughlin,Jerry <
Jerry.Magloughlin at colostate.edu> wrote:

> Two related questions: Is anyone aware of papers describing native iron in
> a wire habit, akin to
> what is sometimes present in native silver and native gold? I have a lot
> of papers on native iron
> and nearly all seem to illustrate or describe a generally granular or
> blocky or irregular habit.
> Second, why does a ‘wire’ habit develop in these isometric minerals? Any
> papers describing this
> would be much appreciated.
> Jerry
> Jerry F. Magloughlin
> Colorado State University
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Peter J. Modreski
U.S. Geological Survey, Denver, Colorado
Office of Communications - Community Relations and Educational Outreach
USGS, Mail Stop 150
Box 25046, Federal Center
Denver, CO 80225-0046
tel. 303-202-4766, fax 303-202-4742
email pmodreski at usgs.gov
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