[meteorite-list] What is and isn't a Widmanstatten Pattern was Cooling rates

[Mr EMan]

--- On Mon, 9/7/09, Jeff Grossman <jgrossman at usgs.gov> wrote:
 <<Most of the metallic minerals in iron meteorites are described as
"alloys" in that they are composed of various metals combined together.>> 

I understood the distinction was that the Fe Ni formed a "chemical compound" not merely a mixture like copper and tin to make brass but even brass can form crystalline plates so that may be a bad example. It was my understanding that were it not for the mineral structure The Fe-Ni would be called an alloy.  Agreed that it is frequently discussed in terms of alloy.

 <<It does not happen as the metal cools from the liquid state and solidifies.>>

I stand corrected, 30 years is a lot of facts to keep in just one's head. I did recall correctly that there is a temperature range and below which all translocation stops. Seems off the top of my head it is 800°C.

<<Goldstein and coworkers have shown that the process is controlled by the Fe-Ni-P phase diagram>>. 

I have long suspected that phosphorus was a key component in the process--likely as a catalyst.  The Schreibersite seems to exist largely at the boundaries in thin laminae even surrounding trolite nodules.  I look forward to reading Goldstein's paper.

Thanks again,
Elton