Definedly wouldn't be practical way to make money, as the deeper you go, the harder it gets to drill since the temperature increases so much that the drill starts melting from the heat and friction. There's a reason why we haven't drilled a hole in the mantle yet, namely it costs a fortune. Altho they're planning it, and think the might start drilling through the oceanic lithopshere sometime between 2015 and 2025. Geothermal power can be obtained by drilling deep holes, but you don't have to go all the way to the mantle for it (just stop at the point drilling starts getting really difficult).
^ There have been several attempts at breaching the Moho discontinuity
(border of crust and mantle) before. Some have claimed to do so but none have been verified.

Basically being to drill holes so deep that it manages penetrate the a planet's crust and reach more or less the upper layers of the molten mantle.
According to The Other Wiki, assuming the composition
is roughly the same as our Earth (give or take a few metallic Phlebotinum), given sufficient energy and technology one can extract more magnesium than simply mining the crust.
Also geothermal power.
What other use is there.
edited 26th Apr '11 8:11:46 PM by Worlder