The Schreger pattern is the recurring light-and-dark motif visible in sections of elephant ivory, the dentine of the tusk. Sections across the tusk can show a checkerboard-like motif, whereas lengthwise sections show alternating bands. This is an example of how the appearance of a three-dimensional biological tissue depends on the plane of observation.[ref]
Relation between the Macroscopic Pattern of Elephant Ivory and Its Three-Dimensional Micro-Tubular Network by M. Albéric and others. Abstract: transverse and longitudinal motifs
In2017, a study based on one elephant tusk compared several section orientations with microscopic observations and computed tomography using synchrotron radiation. The researchers related darker regions to dentinal tubules running obliquely to the cut surface and brighter regions to tubules running more nearly parallel to it. They proposed a three-dimensional tubule arrangement to connect those observations.[ref]
Relation between the Macroscopic Pattern of Elephant Ivory and Its Three-Dimensional Micro-Tubular Network by M. Albéric and others. Materials and Methods: Samples and synchrotron micro-CT; Discussion
The optical mechanism also involves the surrounding material: a2018 study combined X-ray scattering, polarized-light observations and scanning electron microscopy to investigate mineralized collagen orientations. Its authors proposed that the layered collagen architecture and birefringence contribute to the pattern. Thus a visible band is evidence about structure and light interaction, rather than a direct map of a single chemical constituent.[ref]
The three-dimensional arrangement of the mineralized collagen fibers in elephant ivory and its relation to mechanical and optical properties by M. Albéric and others. Abstract: complementary methods, oscillating collagen orientations and proposed optical contribution
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