Tom, Bert, and William Mystery Cache

Cache is not at the posted coordinates! Please do not attempt to access Brunot Island or go swimming in the Ohio River!

Well, aren't you a fine burrahobbit! You swiped the talking wallet, only to find that it's empty! You demand to know where the treasure is. But things can't be that easy, and the wallet responds only in riddles:

CaF2, C, CaSO4·2H2O, SiO2, Re, H2Mg3(SiO3)4, Ca10(PO4)6(OH,F,Cl)2, C, Al2SiO4(F,OH)2, C, C, Mg3Si4O10(OH)2, H2Mg3(SiO3)4, Mn, CaCO3