Atacamite

Atacamite is a copper chloride hydroxide mineral, Cu2Cl(OH)3, first described in 1802 from the Atacama Desert. Wikipedia gives its colour as bright green, dark emerald-green to blackish green, and notes that it has been found as a pigment in sculpture, manuscripts, maps and frescoes. Hall instead describes it as a deep turquoise stone, so the two sources differ on colour. She says it opens the third eye, brings clarity, and helps meditation, visualisation and higher guidance. Cunningham has no entry for it. The pigment use is recorded as a separate form. The magical uses are Hall's beliefs, not demonstrated properties of the mineral.