Gold is mined at thousands of locations on all continents except Antarctica. Placer mining involves sifting and washing sands and gravels to isolate visible gold. Lode or hardrock mining involves crushing rock or soils containing gold and chemically processing the material to extract the gold. The chemical process used prior to the twentieth century was amalgamation, which involves applying mercury to the ore. The gold adheres to the mercury and can then be separated by boiling off the mercury. The amalgamation process is not only inefficient, recovering only about one-half to ...