Imaging some zinc that had been soaked in a phosphate buffered saline-based solution last week, I ran across lots of little zinc phosphate crystals. Two really stood out, and are shaped almost exactly like arrowheads. Far out!
The instrument used was Michigan Tech’s Hitachi S-4700 FE-SEM. Both of these images were captured in “low magnification” mode because the salt crystals are so darn big. They measure a little less than 0.1 mm, and so they are a little smaller than you can see with the naked eye.