Silver is found in the rock galena (lead sulfide).  It contains silver, sometimes in significant quantities.

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"Silver Element Facts." Chemicool. N.p., n.d. Web. 15 Dec. 2013. <http://www.chemicool.com/elements/silver.html>.
"Silver Production | The Silver Institute." The Silver Institute. N.p., n.d. Web. 15 Dec. 2013. <https://www.silverinstitute.org/site/supply-demand/silver-production/>.