G. Zeschke is writing in his article “Simav Graben I ve Taslari” about the turkish fireopal :

“...A Drive from Gediz (Ktahya) after Simav, is passing extended deposits of rhyodacite on both sides of the road. The bright white color of their composits immediately is distinctive.... Just before you reach Simav in this way, the mountains dilate to an elongated Valley, which has an east-west direction approximately . This is a tectonic rift valley, which has a length of over 100 km ...

The Rhyodacite are often intergrown with Opal substance and are silicified. At Oaramanya Ky, this is very nice to see. Here, opal cavity fillings have developed wonderful colors. In earlier times mining for opals of all colors was operating here. Fire opals, precious opal, opalized wood, brown and greenish opals can be found on old dumps...."