Etch figures on the {001}, {010}, {2¯10}, {¯210} and {101} faces of gallium orthophosphate crystals were studied. These were used to detect possible twinning domains. In general, the etch figures exhibited both similarities and differences when compared to those on low-quartz modifications of SiO2 and AlPO4.

Etch Studies of GaPO4 Single Crystals. M.Grassl, R.U.Barz, P.Gille: Journal of Crystal Growth, 2000, 220[4], 522-30