X-ray diffraction refinement of the crystal structure of eosphorite has been carried out with reference to the orthorhombic space group Cmca. The structure is similar to that previously described by Hanson (1960), but the standard deviations are improved. Optical absorption and photoluminescence have also been studied for this mineral. Two sharp emission lines, denoted as R₁ and R₂, superimposed to a broad band (630–750 nm) have been related to the presence of Cr³⁺ ions. The excitation spectrum of these emissions confirms that the absorption (excitation) bands centred at 431 nm and 585 are related to with ⁴A₂ → ⁴T₁ and ⁴A₂ → ⁴T₂ spin allowed transitions of this ion.