Turkish blue Chalcedony does occur in different variants. The term "Chalcedony" is derived from that antique city Chalcedon, the today's Kadikoey - situated to the Bosphorus. In ancient times this was the harbour to ship the anatolian chalcedony from the easternmost province of Turkey.
They seem to be of sedimentary formation and are characterised by a usually spherical shape and superficial contraction-lines. These contractions are enriching the pattern of the polished section. Within the outside range of the blue Chalcedony are snow-like aggregated micro-crystals of rhomboedrical carbonates. They disturb the polishing ability of these zones substantially.
Much of the Chalcedony exported from Eskisehir does not seem to be light stable, i.e. they fade, if they are exposed longer time to the daylight. It seems itself here however not around a UV sensitivity of the material rather than a creeping drainage process to concern.
More informations about todays production of turkish chalcedony is given at www.kalsedon.com.tr