The Jivas (individual living entities - spirit souls) are described as tiny bits of Internal energy. The material energy and the spiritual energy are considered to be the same thing. They are given different designations depending on the situation. For example, food. Once a piece of pie is offered to the Lord it becomes spiritualised and is no longer considered to be comprised of material energy. The substance it is made out of is the same either way. The difference is in it's function or designation. Matter and spirit in Gaudiya siddhanta is relative to the conception of the conscious entity. Atomic particles, molecules, the elements, etc, are only material in the sense of our perception of them.