The image on the cover of the August issue of American Laboratory showed a thin section of granite pegmatite. Pegmatite is an igneous rock composed of interlocking crystals that are usually larger than 3 cm in size. Most pegmatite bodies consist of quartz, feldspar, and mica and are thus considered to be a form of granite. Collectors and miners of gemstones value pegmatites for their large crystals, while granite is commonly used for kitchen countertops because of its strikingly unique appearance and resistance to scratches and burns.
This image was captured by Mark H. Armitage, (Biology Department, California State University, Northridge, CA) using a polarized light microscope under crossed polars. In preparation the subject was thinly polished to approximately 30 μm thickness, mounted to a glass slide, and coverslipped. Original magnification is 250×.