the crystals structure is characteristic of chains with alternating sulfur and mercury atoms, which form helices with the helix axis running parallel to the c axis.
These helices are also the reason why crystals of cinnarbar are optically active (see: A.M. Glazer, K. Stadnicka, “On the origin of optical activity in crystal structures”. J. Appl. Cryst. 19 (2), 1986, 108–122. doi:10.1107/S0021889886089823
The structure is based on a cubic-closest packing of sulfide ions; the copper and iron ions are located in 3/4 of the tetrahedral voids of the packing. At temperatures above 228 °C the cations are completely randomly distributed over these sites (the crystallographer names it disorder), forming a genuine (isometric) cubic phase, but in the low temperature modification the cations are more ordered, which is accompanied with the symmetry reduction to the orthorhombic crystal system