Witherite is an uncommon barium carbonate mineral, BaCO3. It has a nonmetallic, glassy to dull luster, varies in color from clear to white to grayish to yellowish to brownish to greenish, has a white streak, a hardness of 3 to 3.5, and is fairly heavy for its size. Witherite readily bubbles in acid, as do many carbonate minerals. Witherite forms transparent to translucent, columnar-shaped to prism-shaped orthorhombic crystals. These crystals always grow parallel to each other, resulting in pseudohexagonal crystal forms. Witherite does have cleavage, but the twinned nature of witherite crystals prevents easy examination of cleavage planes. Other witherites are massive or granular or fibrous or botryoidal. Perpendicular to the long axis of the pseudohexagonal crystals are obvious striations.
Witherite is a minor ore mineral of barium (the dominant source of Ba is the barium sulfate mineral barite). Witherite is typically found in some low-temperature hydrothermal veins.
Witherite from the Bethel Level, Minerva # 1 Mine, Cave-in-Rock Mining District, southern Illinois, USA. Each hexagonal structure represents twinned witherite crystals, resulting in a pseudohexagonal form. Three crystals make up each hexagonal structure.