The content of barium in the earth's crust is 0.5%. The most common minerals in nature are barite (barium sulfate) and witherite (barium carbonate). Barium compounds are widely used in industries such as glass, glaze, ceramics and rubber to increase the hardness and wear resistance of these materials. Barium compounds are also used to make electronic devices such as disk boards, fluorescent screens and cathode ray tubes. Barium is also used to make alloy materials, such as high-temperature alloys used in the aerospace field. Barium sulfate is used in the petroleum industry to remove barium sulfate precipitates formed in oil wells or underground mining equipment.