Study of the formation conditions and gemology potential of cordierite, Kyanite and Andalusites in the metamorphic aureole of Alvand Complex, Hamedan, Iran

The study area is located in the metamorphic aureole of Alvand Complex Hamedan province. Structurally, the study area is placed in the Sanandaj-Sirjan metamorphic zone. The cordierites in the mesosome of the migmatites have coarse crystals and are accompanied by spinel (lal), which has formed due to the increasing of metamorphism temperature and partial melting processes. The molar fraction (Xmg) of cordierite increases with the increasing degree of metamorphism from the zone of K-feldspar-cordierite to spinel- cordierite (0.45 to 0.620).The approximate temperature for the cordierites in the mesosome of the migmatites is estimated to be 750 ° C and the pressure is ~ 4 kb. Kyanite is specifically hosted by quartz veins in the region, but it is also found in the adjacent of metamorphosed rocks and in the vicinity of veins. The existence of kyanite veins indicates that it's not limited to high pressure facies, but may be formed by hydrothermal pressures. Chiastolite with 20 cm long and 4 cm wide, which is the main outcrop of the Chiastolite schists around Zaman –bad. According to the results of geothermobarometry, the temperature and pressure of Chiastolie schists are 628 ° C, and pressure is about 4 kbar. According to gemology studies, Cordierites are suitable for cabochon and fantasy cut, the high level resistant of this