Abstract: Vertical impact mill for production of very fine powders from larger nut-size pieces of coal, the mill including a series of horizontal impact wheels formed of wheel halves which connected together form an integral shaft-wheel system, the diameter of the impact wheels increasing from top to bottom of the mill, with an inlet at the top of the mill and successive chambers, each housing one impact wheel, and connected by connecting conduits offset from each other by 180.degree.. The mill is designed for use with an inert gas to entrain the powder through and from the mill.