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Old May 21st, 2004, 06:31 AM
GJD GJD is offline
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Originally posted by Straybow:
Undifferentiated is not the same as homogenous; a gob of molten planetstuff can still have a concentration of Ta far above cosmological average.
Indeed it could. However energy sufficent to reduce a planet to plantessimals and then blast them appart with sufficent force to overcome their own mutual gravitational attraction will reduce the planet to a homegenous melt, and will vapourise a good deal of it anyway, which will then condense again as more homogenised melt.

It is the subsequent cooling process which allows the molten tantalum (and other minerals) to form into crystals. One of the major differences between planitessimals and planets is that a planet has sufficent size and mass to retain longer term heat, firstly by attracting other planitessimals which het the main body during impact, and later by radiogenic decay. This longer term heat allows the differentiation process to take place, and the formation of late melt complex minerals.

The proinciple ore of Tantalum is Tantalite, although there are about 20 other tantalum bearing minerals. Tantalite is typically found in pegmatites and other deep crustal rocks which have been upthrust. Its apperance in these massively grained, and hence high tempratyure and pressure deep rocks, shows how it requires a long cooling process to form, and would need a significant impact of a planet to be found in planetessimals.

Smaller planitessimals, whilst they would retain the gross chemical make up of a larger body, would differ in chemistry considerably. However, even if they did form from a Ta rich melt, the melts will still cool much quicker, stunting crystal growth and mineral formation. The Ta would remain locked in a chemically enriched groundmass, whilst the earlier melt minerals such as nickle, iron and so on will form the bulk of the economically viable mineralisation.

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