The Chalcolithic (; khalkós, "copper" and líthos, "stone") period or Copper Age, also known as the Eneolithic or Æneolithic (from Latin aeneus "of bronze"), is a phase of the Bronze Age before it was discovered that adding tin to copper formed the harder bronze. The Copper Age was originally defined as a transition between the Neolithic and the Bronze Age. However, because it is characterized by the use of metals, the Copper Age is considered a part of the Bronze Age rather than the Stone Age.