There are also deposits of Fluorite, Barite, Witherite, Calcite, Dolomite and Barytocalcite. The barium source was either witherite (BaCO) or baryte (BaSO). Witherite forms in low-temperature hydrothermal environments. The rarity of witherite may favor baryte as the most likely source. Witherite was discovered at White Coppice. Witherite crystallizes in the orthorhombic system and virtually always is twinned. Witherite (barium carbonate) was discovered around 1700, and used as a glaze for porcelain. Witherite is a barium carbonate mineral, BaCO, in the aragonite group. Up to this time witherite was considered worthless and used as rat poison by locals. Another commercial source, far less important than baryte, is witherite, a barium carbonate mineral.