Flint.organogenic sedimentary rock composed almost exclusively of silica. The picture shows three chipped flint stones used as tools in prehistoric times. Coming from the hills south of Bologna (Italy)
<a href="//commons.wikimedia.org/wiki/User:Rosapicci" title="User:Rosapicci">Rosapicci</a>
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<span class="int-own-work" lang="en">Own work</span>