- journal_title：Mineralogical Magazine
- Contributor：A. Yu. Likhacheva ; S. V. Rashchenko ; Yu. V. Seryotkin
- Publisher：Mineralogical Society of Great Britain and Ireland
- Date：2012-
- Format：text/html
- Language：en
- Identifier：10.1180/minmag.2012.076.1.129
- journal_abbrev：Mineralogical Magazine
- issn：0026-461X
- volume：76
- issue：1
- firstpage：129
- section：Articles
The elastic and structural behaviour of dehydrated analcime in compression in a non-penetrating medium up to 3 GPa was studied in a diamond anvil cell using in situ synchrotron powder diffraction. A first-order phase transition at 0.4–0.7 GPa is accompanied by a symmetry change from monoclinic (I2/a) to pseudo-rhombohedral (R3) due to trigonalization of the aluminosilicate framework. This is due to the migration of cations to new positions close to the 6-membered rings forming the channels. The reduction of the mean aperture of the structure-forming 6- and 8-membered rings, as a result of tetrahedral tilting, leads to a 7.5% reduction in volume at the phase transition. The bulk modulus values are 38(2) GPa for the low pressure (LP) phase [fitted with a Murnaghan equation of state, K′ = 4 (fixed)] and 11(4) GPa for the high pressure (HP) phase [fitted with a third-order Birch–Murnaghan equation of state, K′ = 9(1)]. The elastic behaviour of the LP phase is anisotropic, with compressibilities βa:βb:βc in the ratio 1:4:2; the most compressible direction b coinciding with the orientation of empty 8-membered rings. The compressibility of the HP phase is isotropic. Trigonalization appears to be the most effective (and probably unique) mechanism of radical volume contraction for the ANA structure type.