High-temperature induced dehydration, phase transition and exsolution in amicite: A single-crystal X-ray study

Pakhomova, Anna S.; Danisi, Rosa Micaela; Armbruster, Thomas; Lazic, Biljana; Gfeller, Frank; Krivovichev, Sergey V.; Yakovenchuk, Victor N. (2013). High-temperature induced dehydration, phase transition and exsolution in amicite: A single-crystal X-ray study. Microporous and mesoporous materials, 182, pp. 207-219. Elsevier 10.1016/j.micromeso.2013.08.036

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Temperature dependent single-crystal X-ray data were collected on amicite K4Na4(Al8Si8O32)·11H2O from Kola Peninsula (Russia) in steps of 25 °C from room temperature to 175 °C and of 50 °C up to 425 °C. At room temperature amicite has space group I2 with a = 10.2112(1), b = 10.4154(1), c = 9.8802(1) Å, β = 88.458(1)°, V = 1050.416(18) Å3. Its crystal structure is based on a Si–Al ordered tetrahedral framework of the GIS type with two systems of eight-membered channels running along the a and c axes. Extraframework K and Na cations are ordered at two fully occupied sites.

Above 75 °C amicite was found to partly dehydrate into two separate but coherently intergrown phases, both of space group I2/a, one K-rich ∼K8(Al8Si8O32) ·4H2O (at 75 °C: a = 10.038(2), b = 9.6805(19), c = 9.843(2) Å, β = 89.93(3)°, V = 956.5(3) Å3) and the other Na-rich ∼Na8(Al8Si8O32)·2H2O (at 75 °C: a = 9.759(2), b = 8.9078(18), c = 9.5270(19) Å, β = 89.98(3)°, V = 828.2(3) Å3).

Upon further heating above 75 °C the Na- and K-phases lost remaining H2O with only minor influence on the framework structure and became anhydrous at 175 °C and 375 °C, respectively. The two anhydrous phases persisted up to 425 °C.

Backscattered electron images of a heated crystal displayed lamellar intergrowth of the K- and Na-rich phases. Exposed to ambient humid conditions K- and Na-rich phases rehydrated and conjoined to the original one phase I2 structure.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Institute of Geological Sciences > Mineralogical Crystallography [discontinued]
08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Pakhomova, Anna, Danisi, Rosa Micaela, Armbruster, Thomas Michael, Gfeller, Frank


500 Science > 540 Chemistry
500 Science > 550 Earth sciences & geology








Frank Gfeller

Date Deposited:

18 Jun 2014 11:21

Last Modified:

05 Dec 2022 14:30

Publisher DOI:


Uncontrolled Keywords:

Amicite, In situ dehydration, Single-crystal X-ray diffraction, Exsolution, Zeolite





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