Fig. 5.

Low-magnification micrograph of a Pinctada fucata shell embedded in epoxy (E), and polished to reveal the cross-section in reflected light. The prismatic (P) and nacre (N) layers are visible, as are the prismatic lamellae (L) on the outer surface of the shell. This image was acquired in reflected visible light, with crossed polarizers, thus calcite crystals with different orientations appear with different gray levels. Notice that some of the prisms (arrows) do not exhibit homogeneous orientation, but are subdivided into domains of different orientations, consistent with the X-PEEM data in Fig. 4. At different angles between polarizers, all the prisms exhibit contrasting intraprism domains.