Summary: Values of Δ2θ131−13¯1(Cu−Kα)(Cu-Kα) have been determined for albites crystallized in the system NaAlSi3O8-β-LiAlSi2O6-H2O at various pressures, temperatures, and times. These values are consistently higher than those reported by MacKenzie (1957) for pure synthetic albites crystallized under similar conditions. Data of the present study have been combined with that of Stewart (1960) for albites crystallized in the system NaAlSi3O8-LiAlSiO4-H2O and, when plotted against bulk Li2O content, show constant Δ2θ131−13¯1 values at approximately 1·0 wt. % Li2O. The addition of Li to albites has a much more pronounced effect on the Δ2θ131−13¯1 parameter than the addition of K or Ca. Albites from lithium-rich pegmatites have much lower Δ2θ131−13¯1 values and are similar to those of synthetic low albites. The differences in this parameter between the natural and synthetic specimens are believed to be caused by differences in the structures of the ceexisting lithium minerals in the natural and synthetic environments.