Cu2Sb-type MgMnGe. P4/nmm #129, Z=2, 6 atoms. a=4.120 Å, c=6.880 Å, c/a=1.670. Antiferromagnetic, TN≈480K. Large local Mn moments. Mg at 2a, Mn at 2c (z≈0.28), Ge at 2b.