Fig. 5

Origin of twinning. a Schematic of twinning in a high chalcocite lattice (S²⁻ shown in blue; Cu⁺ in red). The twin boundary (TB) is denoted by the dotted red line and key crystallographic planes are indicated by dotted yellow lines. b Symmetry relationship of a unit cell of near-orthorhombic djurleite (camel tetragon) to its supercell (green hexagon) of pseudo-hexagonal symmetry⁴¹. a_dj and b_dj are lattice constants of the djurleite unit cell, while a_supercell is the lattice constant of the supercell in the basal plane. The symmetry relationship is possible because a_dj ~√3 b_dj