▁An ▁alk ali ▁earth ▁metal , ▁calci um ▁is ▁almost ▁never ▁found ▁in ▁nature ▁due ▁to ▁its ▁high ▁react ivity ▁with ▁water . ▁It ▁has ▁one ▁of ▁the ▁most ▁widely ▁known ▁and ▁acknowled ged ▁bi ological ▁roles ▁in ▁all ▁animals ▁and ▁some ▁plants , ▁making ▁up ▁b ones ▁and ▁teeth , ▁and ▁used ▁in ▁some ▁applications ▁in ▁cells , ▁such ▁as ▁signals ▁for ▁cell ular ▁processes es . ▁It ▁is ▁regarded ▁as ▁the ▁most ▁abund ant ▁min eral ▁in ▁the ▁body ' s ▁mass . ▁ ▁d - block ▁elements ▁ ▁Sc and ium ▁ ▁Sc and ium ▁( Sc ) ▁is ▁the ▁third ▁element ▁in ▁the ▁period , ▁and ▁is ▁the ▁first ▁transition ▁metal ▁in ▁the ▁periodic ▁table . ▁Sc and ium ▁is ▁quite ▁common ▁in ▁nature , ▁but ▁difficult ▁to ▁isol ate ▁because ▁it ▁is ▁most ▁pre val ent ▁in ▁rare ▁earth ▁comp ounds , ▁which ▁are ▁difficult ▁to ▁isol ate ▁elements ▁from . ▁Sc and ium ▁has ▁very ▁few ▁commercial ▁applications ▁because ▁of ▁the ▁a for ement ioned ▁facts , ▁and ▁currently ▁its ▁only ▁major ▁application ▁is ▁in ▁al umin ium ▁allo ys . ▁ ▁T itan ium ▁ ▁T itan ium ▁( T i ) ▁is ▁an ▁element ▁in ▁group   4 . ▁T itan ium ▁is ▁both ▁one ▁of ▁the ▁least ▁dense ▁met als ▁and ▁one ▁of ▁the ▁strong est ▁and ▁most ▁cor ros ion - res istant , ▁and ▁as ▁such ▁has ▁many ▁applications , ▁especially ▁in ▁allo ys ▁with ▁other ▁elements , ▁such ▁as ▁iron .