gems, turquoise, agate, onyx, amethyst, quartz, jasper, opal, Iran, Persia, Nishapur

Over the past decades, the Geological Survey of Iran (GSI) has conducted many field investigations revealing numerous gemstone occurrences in the Khorasan Razavi Province (KRP) in Northeast Iran. Agate, onyx, amethyst, jasper, opal, rock crystal (clear quartz), rose quartz, orthoclase, tourmaline, fluorite, epidote, garnet group, ilmenite, palygorskite, aragonite, chrysocolla, and turquoise are some of these gemstones. Most of them belong to the silica family formed through magmatic-hydrothermal processes. Geological reconnaissance, including field observations and heavy mineral sampling in several 1:100,000 geologic maps in NE Iran, has proved the presence of economically valuable gemstones of corundum family and beryl. This paper reviews the gemstone potentials of this region, with a special focus on turquoise mineralization. There are many turquoise prospects in the KRP, of which the well-known Nishabur Turquoise is the most important gemstone in Iran. Turquoise is formed as a secondary vein-filling mineral in altered Cenozoic volcanic rocks of The Nishabur Turquoise Mine. This mine is situated in the east of the Cenozoic magmatic belt and is part of the Meshkan Transitional Zone in the eastern Alborz structural zone. According to the latest researches, this deposit is attributed to Iron-Oxide-Copper-Gold deposits. The Nishabur Turquoise has a variety of colors, textures, and qualities, and is categorized based on color, location (mine), and appearance. Geological studies by the GSI have revealed other turquoise deposits in the KRP, including Chah Nasar, Inchegan, Talebi, Saqi Beyg, Zig, Alast Kouh, Aghayeh, and Abgarm. Most of these deposits are all hosted by the Cenozoic volcanic rocks.