<a href="//commons.wikimedia.org/wiki/Basalt" title="Basalt">Basaltic</a> <a href="//commons.wikimedia.org/wiki/Category:Scoria" title="Category:Scoria">scoria</a> (about 8 cm large) coming from <a href="//commons.wikimedia.org/wiki/Category:%C3%8Ele_Amsterdam" title="Category:Île Amsterdam">Amsterdam island</a>  ; blue iridescent color could be caused by interferences phenomenon in a thin and smooth layer of <a href="//commons.wikimedia.org/wiki/Category:Hematite" title="Category:Hematite">hematit</a> (Fe2O3)
<a href="//commons.wikimedia.org/wiki/User:B.navez" title="User:B.navez">B.navez</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>