The intrinsic twinning and enigmatic twisting of aragonite crystals

• 成果类型: Article
• 署名作者: Gavryushkin, Pavel N.; Recnik, Aleksander; Donskikh, Katerina G.; V. Banaev, Maksim; Sagatov, Nursultan E.; Rashchenko, Sergey; Volkov, Sergey; Aksenov, Sergey; Mikhailenko, Denis; Korsakov, Andrey; Daneu, Nina; Litasov, Konstantin D.
• 署名单位: Russian Academy of Sciences; Siberian Branch of the Russian Academy of Sciences; Sobolev Institute of Geology & Mineralogy of the Russian Academy of Sciences; Novosibirsk State University; Slovenian Academy of Sciences & Arts (SASA); Jozef Stefan Institute; Russian Academy of Sciences; Kola Science Centre of the Russian Academy of Sciences; Russian Academy of Sciences; Slovenian Academy of Sciences & Arts (SASA); Jozef Stefan Institute; Vereshchagin Institute of High Pressure Physics, Russian Academy of Sciences; Russian Academy of Sciences
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8893
• DOI: 10.1073/pnas.2311738121
• 发表日期: 2024-02-06
• 关键词: total-energy calculations; x-ray-diffraction; TRANSFORMATION; crystallization; calcite; density

摘要

It is generally accepted that aragonite crystals of biogenic origin are characterized by significantly higher twin densities compared to samples formed during geological processes. Based on our single crystal X-ray diffraction (SCXRD) and transmission electron microscopy (TEM) study of aragonite crystals from various localities, we show that in geological aragonites, the twin densities are comparable to those of the samples from crossed lamellar zones of molluscs shells. The high twin density is consistent with performed calculations, according to which the Gibbs free energy of twin-free aragonite is close to that of periodically twinned aragonite structure. In some cases, high twin densities result in the appearance of diffuse scattering in SCXRD patterns. The obtained TEM and optical micrographs show that besides the twin boundaries (TBs) of growth origin, there are also TBs and especially stacking faults that were likely formed as the result of local strain compensation. SCXRD patterns of the samples from Tazouta, in addition to diffuse scattering lines, show Debye arcs in the a*b* plane. These Debye arcs are present only on one side of the Bragg reflections and have an azimuthal extent of nearly 30 degrees, making the whole symmetry of the diffraction pattern distinctly chiral, which has not yet been reported for aragonite. By analogy with biogenic calcite crystals, we associate these arcs with the presence of misoriented subgrains formed as a result of crystal twisting during growth.