a-quartz, red atoms are oxygens
<a href="https://en.wikipedia.org/wiki/User:Materialscientist" class="extiw" title="en:User:Materialscientist">Materialscientist</a>
2009-12-15
English Wikipedia, <a href="https://en.wikipedia.org/wiki/File:A-quartz.png" class="extiw" title="en:File:A-quartz.png">en:File:A-quartz.png</a>