The As-Cu phase diagram [1988Sub] depicts three intermediate phases: Cu6As (mineral name: algodonite, alg), Cu3As (domeykite, dom), and Cu5As2 (koutekite, kt). Cu6As, with a homogeneity range that includes the composition Cu8As, is a low-temperature phase, forming peritectoidally from (Cu) and Cu3As at 325 °C. Both Cu3As and Cu5As2 have highand low-temperature modifications [1988Sub]. The As-Fe phase diagram [Massalski2] depicts three stoichiometric compounds: Fe2As (Cu2Sb type tetragonal), FeAs (MnP type orthorhombic), and FeAs2 (FeS2marcasite type orthorhombic; mineral name: loellingite, lo). The As-S system [Massalski2] has three intermediate phases: As4S3 (dimorphite, dm), AsS (realgar, rl), and As2S3 (orpiment, orp). There are no intermediate phases in the Cu-Fe system. A metastable liquid miscibility gap is known [Massalski2]. The Cu-S system [1983Cha] is characterized by the presence of two liquid miscibility gaps. The gap at Cu-rich compositions has a monotectic temperature of 1105 °C. Cu1.76-1.79S [CaF2 type face-centered cubic (fcc); mineral name: digenite, dg] forms congruently at 1130 °C. Cu2S (chalcosite, cc) is monoclinic at low temperatures and has the B82 type hexagonal structure between 103 and 435 °C. Above 435 °C, it has the CaF2 type cubic structure and is continuous with digenite. CuS (B18 type hexagonal; mineral name: covellite, cv) forms peritectoidally at 507 °C. There are two intermediate phases in the Fe-S system: the metal-deficient monosulfide Fe1−xS (NiAs type hexagonal; mineral name: pyrrhotite, po) and FeS2 (cubic pyrite, py or orthorhombic marcasite).