= Schreger pattern
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The \b[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.<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]{ref}
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.<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]{ref}
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.<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]{ref}
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