litosphereЛитосфераLITHOSPHERE (Russia)1681-90042500-302XA.N. Zavaritsky Institute of Geology and Geochemistry10.24930/1681-9004-2025-25-2-281-294WFNGVYlitosphere-2276Research ArticleМЕТОДЫ ИССЛЕДОВАНИЯRESEARCH METHODSОсобенности электрофизических свойств гранатов демантоида и андрадита по данным высокотемпературной импедансной спектроскопии: влияние химического состава и фазовых примесей (методические аспекты)Electrophysical properties of demantoid and andradite garnets according to high-temperature impedance spectroscopy data: the influence of chemical and phase impurities (methodological aspects)ЖелуницынИ. А.ZhelunitsynI. A.

620110; ул. Академика Вонсовского, 15; Екатеринбург

Ivan A. Zhelunitsyn

620110; 15 Academician Vonsovsky st.; Ekaterinburg

zhelunitsyn@igg.uran.ruМихайловскаяЗ. А.MikhaylovskayaZ. A.

620110; ул. Академика Вонсовского, 15; 620075; пр-т Ленина, 51; Екатеринбург

Zoya A. Mikhaylovskaya

620110; 15 Academician Vonsovsky st.; 620075; 51 Lenin av.; Ekaterinburg

ВотяковС. Л.VotyakovS. L.

620075; пр-т Ленина, 51; Екатеринбург

Sergey L. Votyakov

620075; 51 Lenin av.; Ekaterinburg

Институт геологии и геохимии им. академика А.Н. Заварицкого УрО РАНРоссияA.N. Zavaritsky Institute of Geology and Geochemistry, UB RASRussian FederationИнститут геологии и геохимии им. академика А.Н. Заварицкого УрО РАН; Уральский федеральный университет имени первого президента России Б.Н. ЕльцинаРоссияA.N. Zavaritsky Institute of Geology and Geochemistry, UB RAS; Ural Federal University named after the First President of Russia B.N. YeltsinRussian FederationУральский федеральный университет имени первого президента России Б.Н. ЕльцинаРоссияUral Federal University named after the First President of Russia B.N. YeltsinRussian Federation202504052025252Минералы: строение, свойства, методы исследования281294Copyright © Желуницын И.А., Михайловская З.А., Вотяков С.Л., 20252025Желуницын И.А., Михайловская З.А., Вотяков С.Л.Zhelunitsyn I.A., Mikhaylovskaya Z.A., Votyakov S.L.This work is licensed under a Creative Commons Attribution 4.0 License.https://www.lithosphere.ru/jour/article/view/2276

   Объект исследования и методы. Методом импедансной высокотемпературной спектроскопии в режиме нагрева-охлаждения при температурах 200–900 °С и частотах 1–106 Гц с использованием электродов из платины и кобальтита лантана-стронция изучены электрические характеристики демантоида из клинопироксенитов (Полдневское месторождение, Средний Урал) и двух образцов андрадита (пробы 1-2) из скарнов (Верхний Уфалей, Средний Урал; Соколовский рудник, г. Рудный, Казахстан). Представлены термогравиметрические и рентгеноструктурные результаты, а также данные диффузионного светорассеяния.

   Результаты

   Результаты. Кристаллохимические формулы андрадита 1-2 и демантоида (Mg0.24Ca3.16Mn0.04)(Fe1.63Al0.33)Si2.95Ti0.05O12.14, (Ca3.49Mn0.04)(Fe1.79Al0.51)Si2.94Ti0.06O12.97, (Ca3.51Mn0.01) Fe2.49Al0.05Cr0.0038)Si3.00O13.34, соответственно. В андрадите 1 фиксируется до ~20 % примеси клинохлора и незначительное содержание примеси ферробустамита; в андрадите 2 – не более ~8 % изоструктурной примеси гидроандрадита; демантоид фазовых примесей не содержит, при этом пики гранатовой фазы ассиметричны вследствие присутствия двух фаз со структурой граната. В оптических спектрах андрадита 1-2 фиксируется широкая полоса в ближней УФ-области и значительное число достаточно широких полос в видимой области, связанных с поглощением ионов Fe2+, Fe3+ и Ti4+; значимого изменения спектра после отжига до 750 °С не происходит; для демантоида фиксируется широкая полоса поглощения 860 нм, которая после отжига смещается до 700 нм; предположено, что полоса 860 нм связана с ионами Cr2+, которые при отжиге испытывают доокисление. Аррениусовские зависимости электропроводности андрадита 1 при нагреве и охлаждении отличны друг от друга за счет наличия в образце примесных фаз (преимущественно клинохлора); аналогичные зависимости для андрадита 2 и демантоида близки друг к другу, при этом электропроводность андрадита 2 выше таковой для андрадита 1. При температурах 750–775 °С демантоид обладает наибольшей проводимостью; при этом примесь Cr не дает значительного вклада в его проводимость.

   Выводы

   Выводы. Впервые получены электрические характеристики демантоида; проанализированы Аррениусовские зависимости двух андрадитов различного химического и фазового состава; показано, что состав оказывает значимое влияние на электропроводимость; полученные данные могут быть использованы для построения геоэлектрических моделей фрагментов земной коры с соответствующими минералами.

   Object of the study and methods. Electrical characteristics of demantoid from clinopyroxenites (Poldnevskoye deposit, Middle Urals) and two samples of andradite 1-2 from skarns (Verkhniy Ufaley, Middle Urals; Sokolovsky mine, Rudny, Kazakhstan) were studied by impedance high-temperature spectroscopy in the heating-cooling mode at temperatures of 200–900 °C and frequencies of 1–106 Hz using of platinum and lanthanum-strontium cobaltite electrodes. Thermogravimetric, X-ray diffraction and diffuse light scattering data are presented.

   Results

   Results. Experimental chemical formulas of andradite 1-2 and demantoid are (Mg0.24Ca3.16Mn0.04)(Fe1.63Al0.33)Si2.95Ti0.05O12.14, (Ca3.49Mn0.04)(Fe1.79Al0.51)Si2.94Ti0.06O12.97, (Ca3.51Mn0.01) (Fe2.49Al0.05Cr0.0038)Si3.00O13.34, respectively. Andradite 1 contains up to ~20 % clinochlore impurity and an insignificant content of ferrobustamite impurity; in andradite 2 – no more than ~8 % of isostructural impurity of hydroandradite; demantoid does not contain phase impurities, while the peaks of the garnet phase are asymmetric due to the presence of two phases with the garnet structure. In the optical spectra of andradite 1-2, a wide band is observed in the near UV region and a significant number of sufficiently wide bands in the visible region associated with the absorption of Fe2+, Fe3+ and Ti4+ ions; Spectra of annealed samples of andradites at 750 °С are similar. For demantoid, a wide absorption band of 860 nm is observed, it shifts to 700 nm after annealing; it is assumed that the 860 nm band is associated with Cr2+ ions, which undergo additional oxidation during annealing. The Arrhenius dependences of the electrical conductivity of andradite 1 during heating and cooling differ from each other due to the presence of impurity phases (mainly clinochlore) in the sample. Dependencies for andradite 2 and demantoid in heating-cooling mode are close to each other, while the electrical conductivity of andradite 2 is higher than that of andradite 1. At temperatures of 750–775 °C, demantoid has the highest conductivity; while the Cr impurity does not make a significant contribution to its conductivity.

   Conclusions

   Conclusions. Electrical characteristics of demantoid were obtained for the first time; Arrhenius dependences of two andradites of different chemical and phase composition were analyzed; it was shown that the composition has a significant effect on electrical conductivity. The obtained data can be used to construct geoelectric models of fragments of the earth's crust with the corresponding minerals.

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The authors declare that there are no conflicts of interest present.