Clinoclase is a hydrous copper arsenate mineral, Cu₃AsO₄(OH)₃. Clinoclase is a rare secondary copper mineral and forms acicular crystals in the fractured weathered zone above copper sulfide deposits. It occurs in vitreous, translucent dark blue to dark greenish blue colored crystals and botryoidal masses. The crystal system is monoclinic 2/m. It has a hardness of 2.5 - 3 and a relative density of 4.3. Associated minerals include malachite, olivenite, quartz, limonite, adamite, azurite, and brochantite among others.