This <a href="https://en.wikipedia.org/wiki/Clay" class="extiw" title="en:Clay">claystone</a> comes from the Underground Research Laboratory sited at Bure in the Meuse district, France, aiming at studying the feasibility of the reversible geological disposal of high-level and long-lived intermediate-level radioactive waste. It is a Callovo-Oxfordian Jurassic marine sedimentary rock formation, grey, about – 165 Ma.
<a href="//commons.wikimedia.org/wiki/User:Cquoi" title="User:Cquoi">Cquoi</a>
<span class="int-own-work" lang="en">Own work</span>