| n. | 1. | (Geol.) A crystalline rock, consisting, like granite, of quartz, feldspar, and mica, but having these materials, especially the mica, arranged in planes, so that it breaks rather easily into coarse slabs or flags. Hornblende sometimes takes the place of the mica, and it is then called |
| Noun | 1. | gneiss - a laminated metamorphic rock similar to granite |