Cu₄Al₂SO₄(OH)₁₂.2H₂O

This sample of cyanotrichite is displayed in the Smithsonian Museum of Natural History. Cyanotrichite is a sulfate mineral of copper with the composition Cu₄Al₂SO₄(OH)₁₂.2H₂O. The sample at left is about 10 cm across and is from Banat, Romania.