Phase stability, elastic behavior, and pressure-induced structural evolution of kalsilite: A ceramic material and high-T/high-P mineral

Abstract

The phase stability, elastic behavior, and pressure-induced structural evolution of a natural metamorphic kalsilite (ideal formula KAlSiO 4 ) from Punalur (Kerala district in southern India), with P31c symmetry and a K/Na molar ratio of ~350, has been investigated by in situ X-ray single-crystal diffraction up to ~7 GPa with a diamond-anvil cell under hydrostatic conditions. At high-pressure, a previously unreported iso-symmetric first-order phase transition occurs at ~3.5 GPa. The volume compression of the two phases is described by third-order Birch-Murnaghan equations-of-state: V 0 = 201.02(1) Å 3 , K T0 = 59.7(5) GPa, K′ = 3.5(3) for the low-P polymorph, and V 0 = 200.1(13) Å 3 , K T0 = 44(8) GPa, K′ = 6.4(20) for the high-P polymorph. The pressure-induced structural evolution in kalsilite up to 7 GPa appears to be completely reversible. The compression of both phases involves tetrahedral rotations around [0001], which close up the channels within the framework. In addition, compression of the low-pressure phase involves tilting of the tetrahedra. The major structural change at the phase transition is an increase in the tilting of the tetrahedra, but with a reversion of the tetrahedral rotations to the value found at ambient conditions. This behavior is in distinct contrast to that of nepheline, which has a tetrahedral framework of the same topology.

High‐pressure behavior and P‐induced phase transition of CaB3O4(OH)3·H2O (colemanite)

“…A mechanism, based on the migration of hydroxyl groups among three different couples of B‐coordination polyhedra and their replacement by H 2 O molecules, is suggested. The high‐pressure polymorph colemanite‐II is characterized by a higher compressibility and by a different elastic anisotropic pattern with respect to the low‐ P polymorph. A similar behavior, though not so common, was already observed in other classes of minerals, in particular in open‐framework silicates . Although the quality of the experimental data prevents a detailed comparative structural analysis, we can, at a first approximation, infer that the P ‐induced strain in colemanite‐II is accommodated by the same general structural mechanisms observed in colemanite.…”

“…A similar behavior, though not so common, was already observed in other classes of minerals, in particular in open-framework silicates. 10,[51][52][53] Although the quality of the experimental data prevents a detailed comparative structural analysis, we can, at a first approximation, infer that the P-induced strain in colemanite-II is accommodated by the same general structural mechanisms observed in colemanite.…”

Isosymmetric pressure‐induced bonding increase changes compression behavior of clinopyroxenes across jadeite‐aegirine solid solution in subduction zones

“…Isosymmetric, “type 0” phase transitions are not uncommon in mineral physics, and as pointed out by Christy [], are necessarily first order only when there are no intermediate lower symmetry states, which might not be observed in experiments. Well‐known examples of type 0 transitions include pressure‐induced layer shift in kaolin‐group phyllosilicates [ Dera et al ., ], pressure‐induced coordination changes of anorthoclase [ Nestola et al ., ] and kalsilite [KAlSiO 4 ] [ Gatta et al ., ], and spin crossover transitions occurring at high pressure in most of iron‐bearing minerals [e.g., Lin and Tsuchiya , ; Lin et al ., ; Speziale et al ., ; Chen et al ., ]. An isosymmetric high‐temperature phase transition was also recently described in orthopyroxene solid solution system [ Ohi and Miyake , ].…”

Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of ane-plagioclase

“…In this section, we have explored how the TO 4 tetrahedra bridge the M sites along the c direction to allow for the propagation of the modulation function, a mechanism similar to that identified in other feldspathoids (Gatta & Angel, 2007;Gatta et al, 2011). This analysis explains why the q-vector of eplagioclase has its strongest component along this direction.…”