Mcguinnessite

IMA formula: CuMg(CO₃)(OH)₂ 

Crystallography: Monoclinic. P2₁/a. a = 12.9181(4) Å, b = 9.3923(2) Å, c = 3.1622(1) Å, β = 111.233(3)°. Z = 4.