The present disclosure relates to a green method for producing and exploiting multiple nano-carbon polymorphs from coal commonly known as anthracite, meta-anthracite, and semi-graphite. The method disrupts the prevalent environmentally unfriendly practices of burning coal with poor profitability and sustainability because the method yields an unexpectedly rich mixture of high-performance nano-materials, comprising carbon nano-fibers, carbon nano-tubes, carbon nano-onions, nano-graphite-plates, and nano-graphene-disks, by simply mechanically-comminuting coal to nano-size, with minimal sorting efforts. The resulting total-yield of nano-carbon polymorphs is over 50% by weight from properly selected coal. Innovative means are added to the prevalent comminution and sorting practices to further reduce energy and chemical consumption. More importantly, the method also refines the comminution and sorting details for producing the best custom-made formulations. This holistic engineering approach eliminates unnecessary separation and sorting steps because a custom-made formulation typically requires blending the sorted components. Formulations with mixed nano-carbon polymorphs are engineered as new and high-valued-added composite ingredients to critically raise the performance of cement-based, polymer-based, and metal-based composites.