mag·ne·sia 
(m
ăg-n
ēzh
ə)
[Short for New Latin magnēsia alba, literally, white magnesia : Medieval Latin magnēsia, mineral ingredient in the philosopher's stone (from Greek magnēsiā, a kind of ore, talc or a talclike substance, after Magnēsiē, a region of Thessaly where it was found, from Magnēs, an inhabitant of Thessalian Magnesia) + Latin alba, feminine of albus, white.]
mag·nesian adj.