Spatial thinking is an essential part of science, technology, engineering, and mathematics (STEM), domains that entail external spatial representations such as 2D graphics, 3D models, and-the focus here-gestures. University students (a) read aloud information about the geological concepts of strike and dip, (b) completed strike and dip tasks, and (c) explained these concepts to another student via audio and video. Gestural patterns varied across reading, audio, and video contexts in interaction with participant variables of spatial skill and prior geology coursework. Only novices gestured during reading, interpreted as novices' attempts to aid their own conceptual understanding of new information. All participant groups produced different gestural patterns in audio versus video contexts, suggesting the communicative intent of many gestures.