Figure A-12. A: Section through a gastropod (snail) shell, in cross-polarized light. The shell consists entirely of aragonite and displays cross-lamellar structure that results in the distinctive zebra-stripe pattern. Circles are artifacts of thin-section preparation. Square outlines approximate area of B.     B: High-magnification image of area outlined in A. Image shows parts of six lamellae in A, and shows that each lamella consists of parallel aragonite crystals (black double-ended arrows are parallel to aragonite crystals). Sub-parallel lamellae in A thus consist of parallel aragonite crystals in B.    Photomicrograph A was taken in cross-polarized light; field of view is 2.2 mm wide. Photomicrograph B was taken in plane-polarized light; field of view is 0.21 mm wide. Modern shells; thin section GPODS. Sample collected by L. Bruce Railsback.
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