Magmatic rock called durbachit observed by 2 nikols. On the thread cross and in the button part are grains of biotite. On the right site are amphibole grains. In the left site is grain of quartz (where the number 20 is) (Zoom in 40 times, 1 millimetre corresponding to 40 units on the scale)
<a href="//commons.wikimedia.org/wiki/User:Chmee2" title="User:Chmee2">Chmee2</a>
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<span class="int-own-work" lang="en">Own work</span>