The alkali metals of Group I are found chiefly as the chlorides (in
the earth's crust and in sea water), and also as sulphates and
carbonates. Lithium occurs as the aluminatesilicate minerals,
spodumene and lepidolite. Of the Group II metals (beryllium to
barium) beryllium, the rarest, occurs as the aluminatesilicate, beryl
magnesium is found as the carbonate and (with calcium) as the
double carbonate dolomite', calcium, strontium and barium all
occur as carbonates, calcium carbonate being very plentiful as
limestone.