Scanning Electron Microscopy of Pirozeh (Turquoise)-group minerals of Nishapur and Baghu (Damghan), Iran

Document Type : Original Research Article

Authors

Department of Geology of Mineral and Water Resources, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

Abstract

Pirozeh (turquoise) is a supergene mineral that forms from meteoric water along fractures which is associated with copper deposits. Although the Persian Pirozeh (turquoise) has been mined since at least the first millennium BCE, it is not a well-known gemstone for geologists. The aim of this paper is about mineralogy and mineral chemistry of the Pirozeh (turquoise) samples of Baghu (Damghan) and Nishapur areas of Iran by using of the scanning electron microscope (SEM). The samples are also analyzed by Energy-dispersive X-ray spectroscopy (EDS) for measuring the major element concentrations of Pirozeh (turquoise) group minerals as well as other mineral phases accompanying them. The results show that the origin of the Pirozeh (turquoise) samples from these areas can be determined by scanning electron microscopy due to their different mineral assemblages and textures. The EDS results suggest that by increasing the Cu content of Pirozeh (turquoise) group minerals their colors move to deeper blue while in contrast green Pirozeh (turquoise) minerals are of notable concentration of Fe. the data propose that the Cu and Fe concentrations of Pirozeh (turquoise) group minerals are not the only factors affecting the color of this gemstone. The geochemistry of Nishapur Pirozeh (turquoise) is defined by high Cu, high Al, and very low Fe/Zn. This results in its celebrated stable blue color. But the Baghu Pirozeh (turquoise) is geochemically distinct due to its higher Fe content. This acts the color from pure blue into the green-blue and green spectrum.

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References

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