Barium

CAS Number: 7440-39-3. A silvery-white metal found in nature.
Barium enters the environment during the mining, refining, and
production of barium compounds, and from the burning of coal and
oil. Barium compounds are used by the oil and gas industries to
make drilling muds. Barium sulfate is sometimes used by doctors
to perform medical tests and to take barium-rays of the stomach.
Chemical formula = Ba. Molecular weight = 137.34 g/mol.