In a moving solution a crystal grows most rapidly on the side that faces the direction of flow. This is because nutrient material is carried to it on this side by bodily movement of solution, and also by diffusion, while on the lee side of the crystal the nutrient material is carried in large part only by diffusion. Thus, the direction of solution movement can often be determined by examination of the growth zones in minerals. This is usually done by sectioning the minerals. Lineages where present may also be used to determine the preferred growth direction. Crystal distortion may also be used. Overgrowths of crusts or scattered small crystals resting on an earlier crystal or other object also afford good evidence. Preferred corrosion or solution of a mineral or mineral aggregate is analogous. The vectorial properties of crystals interfere to some extent.These features have been studied on crystals formed in the laboratory and on many minerals and ores. The experimental work and several examples of ores and minerals are briefly described.