ویژگی‌های کانی‌شناسی، ژئوشیمی، گوهرشناسی و علل تنوع رنگ در آگات‌های میانه، شمال‌غرب ایران

Agate mineralization in the Mianeh area is occurred in the open space filling form in the Eocene volcanic acidic rocks. High potassic and shoshonitic nature of the volcanic rocks have been related to active continental margin setting. The host rocks of the agates are mainly ignimbrite and rhyolite. Blue, red, orange, grey, green and black colors, stelled, cauliflower, fibrous, radiated, circular structures and banded and fibrous textures are seen in the agates. The most important factor causing blue color is copper and for black, red and smoky colors are iron and manganese. Samples have good polishibility and transparency, hardness is 6.7-7 and density is 2.64. Fluorescence and pleochroism features are lacking. The aluminum and volatile amounts show decreasing versus increasing of the silica in the agates. The behavior of REE shows a similar magmatic nature for the studied agates. Practical experiences showed that the best temperature for artificial dyeing for red and orange colors is 500 ºC and for light-dark blue is 550 ºC.