It is assumed that the crystallographic texture of minerals in the shells of recent and fossil mollusks is very stable. To check this, it is necessary to examine the shells of animals that had lain in sediments for millions of years and lived in different conditions. It is revealed that the crystallographic texture of calcite in the shells of Gryphaea dilatata from deposits from the Middle Callovian-Lower Oxfordian (Jurassic), which lived in different water areas, is not affected by habitat conditions and the fossilization process. The crystallographic texture was studied using pole figures measured by neutron diffraction. The neutron diffraction method makes it possible to study the crystallographic texture in large samples-up to 100 cm3 in volume without destroying them. The recrystallization features of the G. dilatata valve, which affect the crystallographic texture, were discovered for the first time. This is determined from the isolines appearance of pole figures. The crystallographic texture of the G. dilatata mollusks' different valves vary depending on their shape. The pole figures of calcite in the thick-walled valves of G. dilatata, Pycnodonte mirabilis, and Ostrea edulis are close to axial and display weak crystallographic texture.
Keywords: Gryphaea dilatata; crystallographic texture; neutron diffraction; pole figures; recrystallization; thick-walled shells.