Electrum (AuAg) is an alloy (mix) of elemental gold and silver with >20% Ag. Most "gold" mineral specimens have some silver mixed in as well. Electrum has a metallic luster, ranges in color from silvery to golden yellow (depending on the silver content), has a high specific gravity (it's heavy for its size), has no cleavage, and is malleable.
Electrum from Oaxaca, Mexico (CSM # 88.37, Colorado School of Mines Geology Museum, Golden, Colorado, USA).
Electrum wires on quartz from the Smuggler-Union Consolidated Mine, Telluride Mining District (aka Upper San Miguel District), eastern San Miguel County, southwestern Colorado, USA. (CSHS # 5610, Colorado State Historical Society specimen, on display at the Colorado School of Mines Geology Museum, Golden, Colorado, USA).