This is the supplementary file for the article "Amorphous Mn2SiO4: A potential manganese phase in the stagnant slab". It includes 5 supplementary texts, 7 figures, and 6 tables. Supplementary texts describe experimental methods, single-crystal X-ray diffraction results, and high-pressure Raman spectra results. Figures show the experimental PT path, crystal structure of tephroite, normalized unit-cell parameters as a function of pressure, pressure independence of polyhedron volume and averaged bond length, pressure dependence of the Raman-active modes for tephroite, amorphous transformation pressure of end-member olivine. Tables describe chemical compositions of tephroite, lattice parameters and unit-cell volumes of tephroite, structure refinement details, best-fit volumetric and linear BM3 parameters, frequency of Raman modes of tephroite.