Structural stabilities of disulfides, diarsenides and sulfarsenides of iron, cobalt and nickel are explained on the basis of ligand field theory, and can be correlated with the number of nonbonding d electrons of the metal atom in the structure, and explained by the tendency of compounds to form structures in which maximum electron spin-pairing takes place. Minerals with pyrite structure are characterized by metal-sulfur octahedra joined at corners, with no apparent interaction between d electrons of neighboring metal atoms. Other structures are characterized by shared octahedral edges along one direction, so that metal atoms are brought into close proximity. In minerals with marcasite structure, there is sharing of octahedral edges, but subtending angles are less than 90 degrees , indicating metal-metal repulsion. In lollingite the large subtending angle and short intermetallic distance signify interaction between adjoining metal atoms.