The largest group of minerals by far is the silicates ( most rocks are â 95 % silicates ) , which are made largely of silicon and oxygen , also with ions of aluminium , magnesium , iron , calcium and other metals . The largest group of minerals by far is the silicates ( most rocks are â 95 % silicates ) , which are composed largely of silicon and oxygen , with the addition of ions of aluminium , magnesium , iron , calcium and other metals .