Pseudomalachite

Pseudomalachite is a hydrous copper phosphate, Cu5(PO4)2(OH)4, prized by collectors as the phosphate cousin of the far more common carbonate malachite. Its name, from the Greek for "false," reflects a similarity in appearance to malachite that once caused decades of taxonomic confusion, until L.G. Berry's 1950 study united several old names — dihydrite, lunnite, ehlite, tagilite and prasin — under the single valid species pseudomalachite. Chemically and structurally it is closely tied to the clinopyroxene-unrelated phosphate group that includes its polymorphs reichenbachite and ludjibaite, and it is isostructural with cornwallite. Colour ranges from blue-green through emerald to a dark, almost blackish green, with a paler blue-green streak, vitreous luster, and a Mohs hardness of about 4.5–5, harder and denser than malachite itself.",

The type locality is the Virneberg Mine at Rheinbreitbach in the Westerwald, Germany, an area of copper mining dating back to Roman times; nearby German classics include the Silberbrünnle Mine near Gengenbach in the Schwarzwald. Other important European sources are Ľubietová (Libethen) in Slovakia, the historic copper mines of Cornwall in England, and Nizhny Tagil in the Russian Urals. Exceptional, gemmy specimens with glossy spherical aggregates of platy crystals come from African copperbelt localities such as Kakanda and M'sesa near Kambove and Mindouli in the Democratic Republic of Congo, and the Bwana Mkubwa and Nchanga mines at Ndola and Chingola in Zambia. Fine American material is recorded from the Empire-Nevada mine in Nevada, the Lone Star and Harquehala mines in Arizona, and the Black Pine Mine in Montana, while Chile contributes specimens from Chuquicamata and Australia from the Burra Burra mine and Spring Creek mine.

Because pseudomalachite forms too irregularly and in too small amounts ever to be mined as ore, its only real value is to mineral collectors, who seek it for its rarity relative to malachite, its rich botryoidal, reniform and radial-fibrous crusts, and occasional rare tabular or prismatic microcrystals. It typically occurs alongside libethenite, cornetite, chrysocolla, azurite and quartz in the oxidised zones of copper sulfide deposits, and specimens showing sharp botryoidal crystal groups or clear associations with these companion phosphates and carbonates are the most desirable for serious systematic and phosphate-mineral collections.