The sources, history of use, preparation, particle and optical char acteristics, chemical properties, and permanence of the blue mineral azurite (basic carbonate of copper) formerly much used as a blue pigment in painting are outlined. The ferrocyanide, triple nitrite, and potassium mercuric thiocyonate tests for copper in microscopicsized specimens of paint films bearing azurite are described. Also spot tests for copper using rubearic acid and ferric thiosulphate can be used. Other methods applied to the identification of copper or the azurite molecule in microscopic specimens are emission spectrometry, x-ray diffraction analysis (spacings and intensities of lines above intensity 20 are listed), and x-ray fluorescence analysis. Blue verditer(artificial basic copper carbonate) is in all respects similar to crushed azurite except in particle characteristics; the particles are fine, rounded and uniform in size. Notable world-wide occurrences of azurite in paintings beginning in ancient times are listed. 1 photograph and 11 photomicrographs in color. 32 references. -- AATA