Dark groundmass is andesite. <a href="//commons.wikimedia.org/w/index.php?title=Amygdaloidal_structure&amp;action=edit&amp;redlink=1" class="new" title="Amygdaloidal structure (page does not exist)">Amygdaloidal structure</a>, vesicules are filled with <a href="//commons.wikimedia.org/w/index.php?title=Zeolite&amp;action=edit&amp;redlink=1" class="new" title="Zeolite (page does not exist)">zeolite</a>. Diameter is 8 cm. Rock sample belongs to the <a href="https://en.wikipedia.org/wiki/en:University_of_Tartu" class="extiw" title="w:en:University of Tartu">University of Tartu</a>.
Photographer: <a href="//commons.wikimedia.org/wiki/User:Siim" title="User:Siim">Siim Sepp</a>, 2005
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>