Calcium is an alkaline earth metal. Alkaline earth metals are those elements whose atoms have their s-subshell filled with their "two valence electrons".
The general electronic configuration of alkaline earth metals is ns2.
They are located on the second column of the modern periodic table and are also called the so-called group two metals.
All alkaline earth metals readily lose their two outermost electrons to form cations with a 2+ charge.
Calcium is an alkaline earth metal, that forms a dark oxide-nitrate layer due to its high reactivity and exposure to air.