1911 Encyclopædia Britannica/Clinoclasite

CLINOCLASITE, a rare mineral consisting of the basic copper arsenate (CuOH)₃AsO₄. It crystallizes in the monoclinic system and possesses a perfect cleavage parallel to the basal plane; this cleavage is obliquely placed with respect to the prism faces of the crystal, hence the name clinoclase or clinoclasite, from Gr. κλίνειν, to incline, and κλᾶν, to break. The crystals are deep blue in colour, and are usually radially arranged in hemispherical groups. Hardness 21/2-3; specific gravity 4.36. The mineral was formerly found with other copper arsenates in the mines of the St Day district of Cornwall. It has also been found 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. The corresponding basic copper phosphate, (CuOH)₃PO₄, is the mineral pseudomalachite, which occurs as green botryoidal masses resembling malachite in appearance.