Turkey is renowned for the agates and thundereggs containing psuedomorphs (calcite and zeolites) inclusions.  Most agates coming from there appear to be a form of weathered thunderegg cores and seams which the shells have mostly been eroded away as a result of exposure to weathering. Some thundereggs have been found intact out of several meters of clay layers that has been decomposed from the rhyolitic lava/tuff beds and there are also some seam agates found nearby.
     The zeolites possibly laumonite sometimes encrusted with calcite have grown in the thunderegg cavities before being replaced and preserved by the gentle sequenced growth of agate. The colors tend to come in white, yellow, light blue, brown, and black. Occasionally, the agates with red to yellow colors have been found.  Some thundereggs contain highly contrasting white and black horizontal layers. The agates tend to be darker inside than what's shown on weathered surface of the roughs.
    Please be aware that black-ish agates with red hollow centers had been found with rhyolitic shells and they can be confused (or passed as) with Crater Agates. It's easy to tell those two apart is that Turkish agates have rhyoltic shells while Crater Agates from Argentina do not have.

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Rough Appearance: Rough agate shapes that is lacking "polygens" structures typical of thundereggs,
Some gray thundereggs have heavily pitted shells. Needle/blade-like structures may show on exposed faces.
Weathered vein agates, the color of agates usually far darker than what's on weathered surface.