Yenisofça / Eskişehir Opal Nodule, Turkey

This beauty is a Yenisofça opal nodule from the Eskişehir area with some quite complex structures - it is not unknown for these to be confused with thundereggs. Especially if, like this one, they contain clear 'cores' or caves. However, these are found in sedimentary rocks rather than volcanic, and common opal replaces an earlier more clay-based nodule (sepiolite). There are references to transparent opal from here, so I am guessing that the clear areas in the centre are still a form of opal - though they could also be chalcedony. An absolutely gorgeous stone, which definitely deserves to be better known.

16cm