The magic of matter is in shaping, refining, combining and transforming. The dwarves have an advanced materials science, though at this historical period they preserve ancient traditions rather than researching new techniques. Their materials are light and strong and exhibit other useful physical properties (insulation and conduction of light, sound, heat and other forms of energy, for example). They craft intricate devices and engines from these materials.
A university-trained human practitioner of matter magic wears a metal bracelet (silver or pewter) set with a yellow stone, such as a citrine or, for the wealthy, a yellow diamond or sapphire. Matter magic is not an especially common subject for human study, but there are practitioners.