The surface of a kidney stone shows tetragonal crystals of Weddellite (calcium oxalate dihydrate). Scanning Electron Micrograph (SEM) taken at 30 KV, horizontal length of the picture represents 0.45 mm of the figured original, image number 10.
<a href="//commons.wikimedia.org/wiki/User:Kempf_EK" title="User:Kempf EK">Kempf EK</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>