Most of us know mercury as the silvery liquid that is in the thermometer.  It is a strange metal, because it is liquid at room temperature, unlike most other metals.  How is it mined if it is liquid at room temperature?  Mercury is not found by itself in nature, but is usually chemically bound with other materials in rock.  The most widespread ore where mercury is found is in a red-colored rock called cinnabar that is sulphur and mercury bound together.  The hills around San Jose, California were a rich source of cinnabar.  It is a very pretty rock, with a reddish, sometimes orange-ish color.  In the hills around San Jose in the Quiksilver Mines County Park, one can find the rock readily.  The native Ohlone Indians of the Santa Clara Valley used cinnabar as jewelry and for make-up to paint themselves, and of course for trading.  Here is a picture of cinnabar ore.

(photo: Mineral Information Institute)

To extract the mercury or quiksilver from the ore, the ore is first crushed and then heated to release sulphur and mercury as a gas.  The gas is then captured and cooled and condensed to form mercury.  The ore is usually readily available near the surface but deep mining can extract rich veins of ore.  The ore is ground to a fine powder, and the heated in a kiln-like furnace.  The mercury can be condensed and collected, and most of the impurities or other contaminating material usually sit on top of the mercury because mercury is very dense.  The impurities are then easily removed, leaving the element mercury (symbol Hg) in a pure liquid form.  

Mercury was used to extract gold and silver from ore during the California Gold Rush.  More interesting though was that the value of mercury from the Quiksilver Mines of San Jose was far in excess of the value of the gold and silver mined from the Sierra.  

The Quiksilver Mines’ fortunes rose and fell with the volatile price of mercury.  Foreign competition and a decline in the price of mercury led the mining company in New Almaden to sell the land and mining facilities to Santa Clara County in 1976.  The mining areas were declared an environmental superfund site, and were cleaned up over the years by remediation efforts.  The property once owned by the mining company — over 4,000 acres — is now one of the largest county parks in the Bay Area.