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Re: Fwd: Question about irons



>
>Steve Schoner wrote:
>
>> I have heard estimates that [Hoba] may
>>have fallen at least 500,000 years ago.
>
>
>Hello Steve, Rob and List,
>
>There is an interesting article in Meteoritics 30-4, 1995
>about the Hoba meteorite with a reference to the terrestrial age:
>
>GOLDEN D.C. et al. (1995) Chemistry and mineralogy of oxidation
>products on the surface of the Hoba nickel-iron meteorite (Meteoritics
>30-4,1995, 418-422):
>
>Hoba is believed to have fallen about or before  8 0 , 0 0 0  years ago
>(McCorkell et al., 1968) in what is now Namibia. The terrestrial age
>was estimated from the 59Ni, a spallation product nuclide.
>

Interesting,  was the 59Ni, nuclide taken from the oxide, and or the
iron?  And what, if any was the degree of uncertianty in the terrestrial
age of the Hoba meteorite?


I would imagine that the results should have taken into account that the
*original*  surface has *rusted* away to some undetermined depth.

Not that I know a great deal about the subject of spallation products
in irons caused by cosmic rays, but to what depth can these products
be produced?  And if the penetration is limited then one would expect
a attenuation of such products the deeper a sample is taken from the
mass in question.

Also, the fact that this meteorite is virtually laying on the surface
would indicate that maybe some erosion has occured, in so far as the
penetration pit, or *crater* if you will has long since vanished.

Just some thoughts.

Steve Schoner, AMS

>And another reference that might be useful:
>
>BUDDHUE J.D. (1957) The Oxidation and Weathering of Meteorites
>(Univ. New Mexico Press, Albuquerque, New Mexico. 162 pp.).
>
>
>Best regards,
>
>Bernd
>
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