Using flux method with cesium chloride solvent, Pb-5(PxAs1-xO4)(3)Cl single crystals were grown. Individual euhedral crystals consist of a hexagonal prism shape topped by a hexagonal pyramid, elongate [001] with a length-to-width ratio of approximately 1:5. These crystals were chemically homogeneous and exhibited no compositional zoning of P and As. Stopping the N-2 supply into the electric furnace during heating and growth formed pale yellow crystals together with colorless transparent crystals. These materials display identical X-ray powder patterns and infrared absorption spectra. Furthermore, no marked difference is apparent in the chemical compositions of colorless crystals and yellow ones. A relationship to color development is apparent in an O1s binding energy in XPS measurements. The O1s binding energy is higher for strongly colored crystals, and that for yellow crystals can shift from 530.65 to 530.73 eV depending on the degree of color development. The O1s binding energies for naturally occurring green pyromorphite and yellow mimetite were greatly enhanced respectively to 531.44 and 531.11 eV. This color development process of materials reflects the environmental concentration of oxygen during its crystallization. (c) 2006 Elsevier B.V. All rights reserved.