Pseudo Polymorphic Transition: the Amphibole→Pyroxene Reaction

Novel extraction route of lithium from α-spodumene by dry chlorination

“…There is also a close resemblance of the resultant products to the reactant which is typical of polymorphic transitions. 50 Using tremolite (the amphibole considered in this study), the decomposition gives rise to diopside and enstatite) ( eqn (18) ) at about 740 °C according to Xu et al 49 Ca 2 Mg 5 Si 8 O 22 (OH) 2 → 2CaMgSi 2 O 6 + 3MgSiO 3 + SiO 2 + H 2 O (g) CaAl 2 Si 2 O 8 → CaSiO 3 + Al 2 SiO 5 …”

“…This implies that, after 850 °C, their transformation to other phases is complete which is in agreement with observation by ref. 50 and 42 . As indicated earlier, the decomposition of mica and amphibole basically form K-feldspar melt and pyroxenes respectively.…”

“…The Gibbs free energy change for the decomposition of tremolite (amphibole) in eqn ( 18) is negative aer 527 C. However, it is an extrapolated data aer 527 C which may be due to either lack of data for tremolite in the soware or its breaks down beyond this temperature. Drawing inference from earlier work, 50 we attribute this to its pseudo-polymorphic decomposition to diopside and enstatite. Extrapolation of data is also observed for albite and spodumene at 927 C as well as annite at 727 C.…”

“…47 Wollastonite, quartz and alkali metal chlorides alongside the synthesized anorthite are products expected at the end of the process (eqn ( 16) and 17). Amphiboles transform to their respective pyroxenes and quartz through topotactical dehydration decomposition at temperatures above 600 C. [48][49][50] The transformation is pseudopolymorphic because it occurs at a xed temperature for a given pressure. There is also a close resemblance of the resultant products to the reactant which is typical of polymorphic transitions.…”

Shock-metamorphic features in amphiboles from the Xiuyan crater of China

“…quartz ? H 2 O at temperatures above 700°C (Deer 1963;Freeman and Frazer 1968;Xu et al 1996;Inoue et al 1998;Evans 2007). Shock loading experiments showed that amphibole can transform into an amorphous b Backscattered electron image of shocked amphiboles shows that the patch is composed of a number of micrometer-sized dendrites of pyroxenes (Px) associated with interstitial silicate glass Fig.…”