Citation: Pakhnevich, A.; Nikolayev, D.; Lychagina, T. Global Crystallographic Texture of Pyrite in Fossil Wood (Jurassic, Oryol Region, Russia). Minerals 2023, 13, 1050. https://doi.org/10.3390/ min13081050 Academic Editors: Olev Vinn, Daniel Acosta-Avalos and Fernanda Abreu Received: 28 June 2023 Revised: 25 July 2023 Accepted: 4 August 2023 Published: 8 August 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). minerals Article Global Crystallographic Texture of Pyrite in Fossil Wood (Jurassic, Oryol Region, Russia) Alexey Pakhnevich 1,2 , Dmitry Nikolayev 2 and Tatiana Lychagina 2, * 1 Borissiak Paleontological Institute, Russian Academy of Sciences, 117647 Moscow, Russia; alvpb@mail.ru 2 Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia; dmitry@nf.jinr.ru * Correspondence: lychagina@jinr.ru Simple Summary: Fossil wood of the Jurassic period from the Oryol region, Russia was studied using a non-destructive method. The method is based on the high penetrating power of neutrons into matter. The organic matter of the wood was replaced by the mineral pyrite. The distribution of pyrite crystal orientations in the fossil wood and pyrite nodules from the same locality was compared. It was found that mineral crystals replacing fossil wood are more ordered than these mineral crystals in the nodules. This fact confirms the idea that, in the future, using an organic matrix, it is possible to grow crystals in given directions, planning in advance the properties of new materials. It was also concluded that one can assume the origin of the studied objects by analyzing the distribution of their crystal orientations. It may be useful in the search for mineral matter of biogenic origin. Abstract: Many works are devoted to the study of the crystallographic texture of primary skeletal minerals of animals. But how the directions of mineral crystals that replace the organic matter in the fossil state are oriented is unknown. Here we investigated the crystallographic texture of pyrite grown on an organic matrix and without it. Jurassic pyritized wood (Middle Jurassic, Callovian) was studied by the neutron diffraction method. The global crystallographic texture of pyrite in nodules and fossil wood is compared. It was found that in both cases, the isoline patterns of pole figures and texture sharpness are similar to the same characteristics of abiogenic calcite. But the orientations of pyrite crystals in wood are more ordered, the isolines are closer, and the regions of maximum pole density are wider. That is, the pyrite crystals that replaced the petrified wood are more ordered. This was influenced by the organic matrix on which the crystals grew. Repetition of a fossil mollusk shell shape without using its shell as a matrix for crystal growth does not lead to an increase in the crystallographic texture sharpness. This is illustrated by an example of the inner core calcite shell of the gastropod mollusk Bellerophon sp. Keywords: crystallographic texture; neutron diffraction; pole figures; fossil wood; pyrite; Jurassic 1. Introduction Organic compounds are destroyed often after the death of the organism and are not preserved in the fossil record. However, in some cases, the organic or its derivatives are preserved; for example, chemofossils are fragments or whole molecules of biogenic origin. Natural polymers such as cellulose, lignin, and sporopollenin are often preserved in the fossil state. Therefore, some plant remains are well preserved, almost unchanged for millions of years; for example, wood. In other cases, it can be charred, that is, a significant part of the organic matter turns into carbon or wood is replaced by minerals. The range of these minerals is significant, namely quartz [1], opal, pyrite, marcasite, volkonskoite, siderite, malachite, azurite and apatite, chalcedony, calcite, dolomite, hematite, goethite, hollandite, lepidocrocite, chalcopyrite, chalcocite, bornite, covellite, fluorite, barite, natrolite, Minerals 2023, 13, 1050. https://doi.org/10.3390/min13081050 https://www.mdpi.com/journal/minerals