The largest known mine is the Rio Tinto Borax Mine in Boron, California. The reserves in this mine are expected to last until 2050. The chemical formula for borax is Na 2 B 4 O 7 ·10H 2 O. In more simple terms, this includes sodium, boron, oxygen, and hydrogen. Borax has a number of different names, but they are all the same chemical compound. ...