CuSiO3-nH2O. A sky blue mineral composed of hydrated copper silicate. Chrysocolla is a secondary copper ore that has also been used as a gemstone and a blue-green pigment. It has been gathered or mined as a semiprecious stone since 3000 BCE. Chrysocolla is mined in Cornwall, Cumberland, Congo, Chile, and the U.S. (Pennsylvania, Arizona, New Mexico and Utah). The translucent to opaque stone is sky-blue in its natural state, but appears green when ground into a fine powder. Chrysocolla has been found as a pigment in wall painting at Kizil in Turkistan and in Twelfth Dynasty Egyptian tombs (Gettens and Stout 1966). In the 16th and 17th centuries, it was used as a watercolour pigment called cedar green. Chrysocolla is stable to light but is decomposed by acids, alkalis and heat. Synonyms: cedar green; copper silicate. Gettens and Stout (1966); Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]