Seth Frank (Thin Section Laboratory, IODP JRSO) operates some of the precision equipment used to fabricate petrographic thin sections. Successful thin section production requires a delicate touch as they are ground and polished to 30 microns, about the thickness of a human hair. The finely ground sections of rock show distinct colors and characteristics when scientists view them through polarized light. Trained petrologists use these thin sections to identify minerals in the sample as well as hints about how it formed, such as when it solidified from a liquid into crystals, at what depth it was formed beneath the Earth’s surface, etc. (Credit: William Crawford, IODP JRSO) [Photo ID: exp367_163]