Leightonite
Leightonite is a rare sulfate mineral with formula of K2Ca2Cu(SO4)4•2H2O.
Leightonite forms flattened to elongated bladed crystals of variously interpreted crystal structure. Its crystal system is reported as triclinic morphologically, but also as pseudo-orthorhombic due to intricate lamellar twinning that mimics orthorhombic symmetry. Because it is triclinic, the crystal is represented by a system of three unequal vectors with corresponding unequal angles between them.