= Rare Earths, Magnets, etc. =

High intensity magnets are currently made with rare earth elements.  REEs principally occur in monazite.  According to [[attachment:Thorium.pdf|this paper]], there is 1 megatonne ( 1e9 kg ) of thorium (and presumably rare-earth bearing) ores.  Presume monazite ores, which are 5% to 10% thorium oxide, and 55% to 60% rare earth oxides.  Another source (used below) cites 99 megatonnes of rare earth ore, though these ores may be marginally beneficiated (naturally concentrated). The following assumes 99 MT of 55% REO.

The crustal abundance of rare earths is (presumably ppm by weight):

|| Element            ||   ppm ||   frac || AMU ||    PO4 ||  monaz ||   1 MT ||  99 MT ||
|| Cerium             ||  60.0 || 0.2946 || 140 || 0.1191 || 0.0979 ||  33 KT || 3.2 MT ||
|| Yittrium           ||  33.0 || 0.1620 ||  89 || 0.0836 || 0.0539 ||  17 KT || 1.7 MT ||
|| Lanthanum          ||  30.0 || 0.1473 || 139 || 0.0598 || 0.0490 ||  16 KT || 1.6 MT ||
|| '''Neodymium'''    ||  28.0 || 0.1375 || 144 || 0.0546 || 0.0457 ||  15 KT || 1.5 MT ||
|| Scandium           ||  20.0 || 0.0982 ||  45 || 0.0666 || 0.0326 ||  11 KT || 1.1 MT ||
|| '''Praseodymium''' ||   8.2 || 0.0403 || 141 || 0.0162 || 0.0134 ||   4 KT || 0.4 MT ||
|| '''Samarium'''     ||   6.0 || 0.0295 || 150 || 0.0114 || 0.0098 ||   3 KT || 0.3 MT ||
|| Gd Dy Yb Er        ||  14.2 || 0.0697 || 157 || 0.0263 || 0.0232 ||   8 KT || 0.8 MT ||
|| Eu Ho Tr Tm Lu     ||   4.3 || 0.0211 || 152 || 0.0081 || 0.0070 ||   2 KT || 0.2 MT ||
|| Total              || 203.7 || 1      ||     || 0.4458 || 0.3325 ||        ||        ||
|||||||| Fraction metals                        || 0.5542 ||        ||        ||        ||
|||||||| Fraction metals 55% RE monazite        || 0.3325 ||        || 109 KT ||  11 MT ||

The mass percentage assumes the mineral is a PO₄ phosphate (95 AMU ).

The crustal abundance is used here as a proxy for relative abundance in REE ores.  Most of the REEs are ''not'' concentrated into ores, and are ''not'' economically recoverable (we cannot afford to run the entire earth's crust through magnetic separation - not enough magnets!).  None are concentrated in other solar system objects, none of which have plate tectonics, granite, oxygen-bearing atmospheres, and ocean-driven beneficiation.

|| Major deposits || MT ||
|| China          || 36 ||
|| United States  || 13 ||
|| Australia      ||    ||
|| India          ||    ||
|| World          || 99 ||
[[ http://www.ibtimes.com/2011-spells-desperate-search-rare-earth-minerals-253177 | Questionable source ]]

A [[ http://www.reuters.com/article/2009/09/02/retire-us-mining-toyota-idUSTRE57U02B20090902#yHQastzfHFpQpbcW.97 | Prius uses ]] 1 kg of neodymium in the motor, and 10 kg of lanthanum in the battery.  Assuming 99MT of 55% REO ore, there are enough reserves of lanthanum-containing rare earths worldwide to produce only 160 million Priuses of the current design.  The neodymium stretches farther - 1.5 billion Priuses - and praseodymium and samarium can also be used for high-strength magnets.

Launch loop magnet rails will also require high-strength magnets.  Those will be recycled, but some will be lost.  Presume that skyrocketing rare earth prices will drive frantic research for clever nanomaterial substitutes, which allow us to make high-energy-density magnets with more abundant materials.