Iron Lattice (was earth/moon relationship)

James Rogers (
Wed, 29 Oct 1997 11:59:56 -0800

At 10:36 AM 10/29/97 +0100, Anders Sandberg wrote:
> writes:
>> And I heard (somewhere,can't remember, no references..but
>> that some evidence had been "unearthed" that the core of the earth was a
>> single (huge) iron crystal...
>> In accordance with principles set forth in "Demon Haunted World" this
>> bogus? or actually possible.
>I'm not sure, and I'm not a geologist, astrophysicist or even a
>physicist, but I would argue it is unlikely. The core is believed to
>contain not just nickel-iron, but other heavy elements. This suggests
>to me that the core cannot form a nice crystal lattice, and likely has
>an amorphous structure. But a lot likely depends on the behavior of
>this mixture at high pressures and temperatures; things can get rather
>counterintuitive down there, so I wouldn't be totally surprised if it

It is very possible to form crystal lattices using a mixture of different
elements, especially with metals. In fact, some alloys (eutectics) exhibit
the same phase behavior as pure metals. Iron is generally an easily
alloyed metal, probably due to the fact that it switches crystal structures
(between BCC, FCC, and HCP) easily under fairly mild conditions. As for
amorphous crystals, I don't think metal crystals can be amorphous. If I am
not mistaken, amorphous crystals can only occur when there is little or no
electron mobility in the lattice, which is not the case with metal crystals.

Additionally, high temperature/pressure environments are *ideal* for large
crystal growth. The high temperature means the atoms have enough energy to
organize, and the high pressure strongly encourages the formation of large
crystal lattices. When you consider that the core pressure is around 50
million psi, it would be nearly impossible for amorphous crystal structures
to occur, especially when you have the atomic mobility that occurs at a
temperature of 5000-6000 C.

-James Rogers