A famous mine near the Continental Divide at Climax, Colorado, is a major source of the world's supply of molybdenite. Although galena's principal constituent is lead, it often is an important source of silver because it contains silver as an impurity. A variety of uraninite known as pitchblende was once thought to be worthless. With the dawn of the atomic age it became one of the most sought-after minerals in the world. Quartz contains silicon and is one of the most common minerals.
Many beach sands consist of nearly pure quartz.
Check out the various definitions of mineral at the Mineral Database and learn that even the definition of minerals can be very complex. While you're at it, check out some striking pictures of mineral specimens.