There are materials that exist in unusual solid-liquid hybrid phases, for example, the superionics at high temperatures of 700 °C. Using ab initio molecular dynamics, we show that the intensely studied Cu(2)S high chalcocite phase is actually a solid-liquid hybrid phase which exists in relatively low temperature (>105 °C). Its formation mechanism is different from the superionics. We also show that the previously proposed atomic structure for high chalcocite is incorrect, and the low chalcocite to high chalcocite transition should be described as a sublattice solid to liquid transition.