Final answer:
Anorthite is the mineral that represents the calcium endmember of the plagioclase series found in mafic igneous rocks and lunar rocks.
Step-by-step explanation:
The mineral that represents the calcium endmember of the plagioclase series is anorthite. In the plagioclase feldspar series, anorthite (CaAl2Si2O8) is the calcium-rich endmember, while albite (NaAlSi3O8) is the sodium-rich endmember. The series is a solid solution and the minerals vary in composition between these two endmembers. Anorthite is found in mafic igneous rocks and is a common component of lunar rocks.