Cover image from October 1972 issue of the National Geographic Journal Vol. 142, No. 4.

Fluid as water, brilliant as silver, heavier than lead, mercury spills through a mine worker's fingers. A unique element — the only metal that is liquid at room temperature — mercury has fascinated mankind for centuries. Ancients used its compounds for medicines and pigments. Today thousands of products — from thermometers and light switches to pesticides — depend on its unusual properties. But recent tragedies, caused by rising levels in the environment, have shown that mercury can be a deadly servant.