A waste majority of crystals exists in several polymorphic forms in different domains of the P,T-diagram. Liquids and glasses also exhibit polyamorphism and the question remains whether the liquid-liquid transformation appears to be a first-order phase transition. The mercury thioarsenate glasses seem to show a different phenomenon: an instantaneous mercury sulphide dimorphism. Our Raman spectroscopy measurements and DFT modelling first exhibit a hybrid Hg-S chain/As-S pyramidal network. Nevertheless, the preliminary high-energy x-ray diffraction measurements suggest also the presence of Hg-S tetrahedra. The proposed ND experiments on HgS-As2S3 liquids and glasses using GEM or SANDALS together with complementary HE-XRD experiments and EPSR/RMS modelling will greatly advance our understanding of these important functional materials and the exciting phenomenon of polyamorphism.