A twinned (NH4)3H(SeO4)2 crystal under the polarizing microscope at room temperature. (Figure 1 from my publication No. 17. See left.)
Publications
These research graphs from my PhD thesis are embodied in Michael O’Keeffe’s book.Structure and Bonding in Crystals Vol. 1, and B. K.Vainshtein’s Modern Chrystallography Vol. 2