October 2015 Microphoto of the Month
Deformed plagioclase Cross-polarized light, 50x.
Most people think of rocks as brittle things that fracture (if you hit them hard enough!). However, under certain circumstances, usually involving the slow application of stress at high temperature, rocks can actually flow. The bent areas of this crystal of plagioclase feldspar were straight lines when the crystal formed, but became curved as they deformed under pressure. Although it seems strange for a solid to flow, think of a wire. Most metals can be easily bent without breaking them. It may be a little harder to do that with rocks, but it can happen under the right conditions.