III.

Occurrence

Silver ranks about 66th among elements in natural abundance in crustal rocks. It occurs in the pure state to a small extent; the most notable deposits of native silver are in Peru and Norway, where the mines have been worked for centuries. Pure silver is also found associated with pure gold in the form of an alloy known as electrum, and considerable amounts are recovered in the processing of gold. Silver is usually found combined with other elements (of which sulfur is the most predominant) in minerals and ores. Some of the important silver minerals are cerargyrite (or horn silver), pyrargyrite, sylvanite, and argentite. Silver also occurs as a constituent of lead, copper, and zinc ores, and half the world production of silver is obtained as a by-product in the processing of such ores. Practically all the silver produced in Europe is obtained from the lead sulfide ore, galena. In the United States relatively few mines are worked for their silver alone—the silver is mined in conjunction with lead, copper, and zinc. In 2004, U.S. mines produced 1,250 metric tons of silver, about one-eighth of the production worldwide. Most of the silver mined in the world comes from Mexico, the United States, Peru, Australia, and Canada. The leading silver-producing states in the United States are Nevada, Idaho, Alaska, and Arizona.