Oxychlorides – Atacamite and Hydrous Chlorides – Carnallite

Atacamite
Composition. Copper chloride with copper hydroxide, CuC1₂.3Cu(OH)₂ = Chlorine 16.6, copper 14.9, cupric oxide 55.8, water 12.7.

Crystallization. Orthorhombic. Commonly slender prismatic in habit, whit vertical striations. Also tabular parallel to brachypinacoid.

Structure. In confused crystalline aggregates; fibrous, granular. As sand.

Physical Properties. Cleavage perfect parallel to brachypinacoid. H. = 3-3.5.  g. = 3.75-3.77. Adamantine to vitreous luster. Color various shades of green. Transparent to translucent.

Test. fusible (3-4), giving an azure-blue flame of cooper chloride. B.B. on charcoal with sodium carbonate gives globule of copper. Nitric acid solution with ammonia in excess gives blue solution. Gives acid water in C.T. Characteristic by its green color and granular crystalline structure. Distinguished from malachite by its lack of effervescence in acids.

Occurrence. A comparatively rare copper mineral. Found originally as sand in the province of Atacama in Chile. Occurs with other cooper ores in various localities in Chile. Occurs with other copper ores in various localities in Chile and Bolivia. Found in some o f the copper districts of South Australia; occurs sparingly in the copper districts of Arizona.

Use. A minor ore of copper.

Hydrous chlorides: Carnallite
A hydrous chloride of potassium and magnesium, KC1. MgC1₂.- 6H₂O. Orthorhombic. Massive, granular. Crystals rare. Luster nonmetallic, shining, greasy. Color milk-white, often reddish, due to included hematite. Transparent to translucent. H. = 1. G. = 1.6 Bitter taste. Deliquescent. Fusible at 1-1.5 with violet flame. After ignition gives an alkaline reaction on moistened test paper. Easily and completely soluble in water; on addition of nitric acid and silver nitrate gives a white precipitate of ammonium magnesium phosphate. Found associated with halite, sylvite, etc., in the salt deposits at Stassfurt, Prussia. Used as a source of potassium compounds.