Earthworms eat organic matter, along with soil, and leave behind castings. Apart from microbial decomposition of organic matter, the additional activity in the earthworm's gut, creates a richer compost.
Red worms, "red wigglers" (Eisenia fetida) are surface dwelling worms, that is generally used in vermi-composting. Subhash Palekarji , proponent of Zero Budget Natural Farming, doesn't recommend these worms. Irrespective of the type of worm used, they seem to benefit from trace minerals in rock dust.
Organic waste, and domestic sewage water were converted into high quality soil for raising seedlings, by the addition of rock dust in a Brazilian study