Optical properties of synthetic crystals of brushite (CaHPO4·2H2O)

The principal refractive indices of brushite (CaHPO4·2H2O) crystals for sodium light, 589 nm, have been determined by a combination of several methods: microscopic interferometry, retardation measurements with an Ehringhaus 6λ compensator, and determination of the angle 2V between optic axes from the measurements of extinction directions using a spindle stage and evaluating the data with the computer program EXCALIBRW. The following values were found: nα=1.54089, nβ=1.54620, nγ=1.55191, and 2V=88.2°. The standard deviations of the three indices lie in the range 7–8×10−5. The results are regarded valuable in connection with studies of crystal growth kinetics in biological mineralization and related fields.