TY - JOUR

T1 - The intrinsic twinning and enigmatic twisting of aragonite crystals

AU - Gavryushkin, Pavel N

AU - Rečnik, Aleksander

AU - Donskikh, Katerina G

AU - Banaev, Maksim V

AU - Sagatov, Nursultan E

AU - Rashchenko, Sergey

AU - Volkov, Sergey

AU - Aksenov, Sergey

AU - Mikhailenko, Denis

AU - Korsakov, Andrey

AU - Daneu, Nina

AU - Litasov, Konstantin D

N1 - We thank the Information Technology Centre of Novosibirsk State University for providing access to the cluster computational resources. P.N.G., K.G.D., M.V.B., and N.E.S. was supported by state assignment of IGM SB RAS (122041400176-0). A.K. was supported by state assignment of IGM SB RAS (122041400241-5). D.M. was supported by state assignment of IGG UB RAS (AAAA-A19-119072990020-6 to D.M.). The transmission electron microscopy (TEM) analyses were conducted within the framework of the Slovenian-Russian BI-RU/16-18-004 "Crystallography, twinning and phase transformations in minerals with aragonite structure" program and project "Aragonite: structure and formation", supported by a Hungarian-Slovenian bilateral fund (grant no. SNN-139585 at the National Office of Research, Development and Innovation (NKFIH) of Hungary and N1-0230 at the Slovenian Research Agency (ARRS). A part of X-ray diffraction (XRD) characterization was done using the equipment of Research and Education Centre "Molecular Design and Ecologically Safe Technologies" at Novosibirsk State University. The samples of aragonite from Spanish localities were provided by Jose Ramon Pastor of Trencapedres Minerals (Alicante, Spain) and by Victor Yakovenchuk (Kola Science Center, Russia); the specimen from the Koge-Dava-by Andrey Vishnevskiy, the director of the Central Siberian GeologicalMuseum(Novosibirsk); the illustration of twined aragonite in Fig. 1-by Mirjan Žorž.

PY - 2024

Y1 - 2024

N2 - 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 [Formula: see text] plane. These Debye arcs are present only on one side of the Bragg reflections and have an azimuthal extent of nearly 30°, 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.

AB - 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 [Formula: see text] plane. These Debye arcs are present only on one side of the Bragg reflections and have an azimuthal extent of nearly 30°, 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.

KW - DFT calculations

KW - diffuse scattering

KW - strain

KW - twinning

KW - twisting

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85184104659&origin=inward&txGid=ff21be7f999c914d89325d0574840167

UR - https://www.mendeley.com/catalogue/01d821ac-8a4b-3f21-b01f-b2dc305e8f34/

U2 - 10.1073/pnas.2311738121

DO - 10.1073/pnas.2311738121

M3 - Article

C2 - 38300859

VL - 121

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

SN - 0027-8424

IS - 6

M1 - e2311738121

ER -