Phase equilibria in the join CaCaSiO₄-CaCrCrO₄ were investigated by the quenching technique. Although the maximum solubility of CaCrCrO₄-component to calcium orthosilicate was not determined because of experimental difficulties, it is estimated to be less than 9 wt percent for α form. The solbility in α form is 8.1 wt percent as much at 1500°C and that in α' form is 1.9 wt percent as much at 1100°C. In the moderate temperature region there is α wide range of coexisting region of α form and α' form. Calcium orthosilicate solid solutions are quenched usually as β forms. However, high temperature modification of α form is preserved to room temperature partly or almost entirely, when CaCrCrO₄ content exceeds 4 wt percent. The crystalline phases are α calcium orthosilicate solid solution, α' calcium orthosilicate solid solution and β calcium chromite in the investigated temperature. The calcium orthosilicate solid solutions of α form and β form after α form are green in colour, while those of β form after α' form are bluish green in colour. Subsequent measurement of optical spectra for the Cr-bearing calcium orthosilicate was made in wavelength range of 325-2600 nm. Crystal-field interpretation shows that Δt and B are ranging in 13800-13920cm^-1 and in 460-464cm^-1 for β forms, respectively, and are 13710cm^-1 and 457cm^-1 for α form, respectively. Assignment of bands indicates that tetrahedral Cr³⁺ ions may be present in low spin state as suggested by Ikeda and Yagi (1977) for Crbearing blue diopsides.