n.1. A small stone, especially one worn smooth by erosion.
2. a. Clear colorless quartz; rock crystal.
b. A lens made of such quartz.
3. Geology A rock fragment between 4 and 64 millimeters (0.16 and 2.51 inches) in diameter, especially one that has been naturally rounded.
4. An irregularly rough, grainy surface, as on leather or paper.