Gneisses are classified based upon a variety of characteristics, such as constituent minerals, parent materials, and chemical composition. Some, such as augen gneiss, are also described based upon their structure. This type of gneiss gains its name from the elliptic or lens-shaped form of many of its mineral grains. Indeed, the word augen is German for “eye,” a reference to the appearance of these readily visible components of metamorphic rocks. To some people, an augen structure appears more akin to nuts than eyes. In fact, the scenic Hickory Nut Gorge in North Carolina is believed to have been named for the nut-shaped minerals found in much of the exposed rock present in that location.