CLINOCLASITE, a rare mineral consisting of the basic copper arsenate It is deep blue in colour and crystallizes in the monoclinic system with a perfect cleavage parallel to the basal plane ; hardness 2 2-3 ; specific gravity 4.36. The mineral was formerly found with other copper arsenates in the mines of the St. Day district of Cornwall and near Tavistock in Devonshire, near Sayda (or Saida) in Saxony, and in the Tintic district of Utah. It is a mineral of secondary origin, having resulted by the decomposition of copper ores and mispickel in the upper part of mineral veins.