The Behavior of Water in Orthoclase Crystal and Its Implications for Feldspar Alteration

Abstract

The phenomenon of feldspar alteration that occurs in the interior of feldspar crystals remains poorly understood. We observed experimentally that water can go into orthoclase crystals under pressures of up to 600 MPa at room temperature. With increasing pressure, the FTIR spectra of colorless orthoclase show a sharp increase in integral absorbance from 1.50 cm−1 to 14.54 cm−1 and normalized integral absorbance from 120 cm−2 to 1570 cm−2; the pink orthoclase saturates quickly with no significant change in either the integral absorbance or normalized integral absorbance. The different responses to the pressure between colorless orthoclase and pink orthoclase might be related to the K content in the structure. Moreover, FTIR spectra at atmospheric pressure collected in different crystallography directions show different absorbance intensities, which illustrates the characteristic of preferred crystallographic orientations. These results reveal that H2O molecules can occur as structural constituents entering the crystallographic channels of alkali feldspar crystals, preferentially along (001) orientation. These findings provide clues into the mechanism of feldspar alteration occurring in the interior of feldspar crystals, as well as the formation of micropores and microstructure in feldspar minerals. This study also provides important insights into the behavior of water molecules in nominally anhydrous minerals in the upper crust of the Earth.

Mineralogical Crystallography Volume II

“…Using FTIR, Zuo et al [8] have found the presence of H 2 O molecules in the crystal structure of alkali feldspar within channels with preferable (001) orientation. It is suggested that this water plays an important role in the mechanisms of feldspar alteration and water preservation in nominally anhydrous minerals in Earth's depths.…”

The Micromorphology of an Sensisitve Hilly Soil as Habitat for Microbiota Delivering Soil Ecosystem Services

“…The translocation process is directly influenced by the both vertical and lateral water movements in the soils located on a slope. Among the multitude of the mineral skeleton grains of the soils, the feldspars are also present, being affected by the sericitization process, a very common hydrothermal alteration (Zuo et al, 2016;Zuo et al, 2022) and also an ubiquitous characteristic (Verati and Jourdan, 2014;Zuo et al, 2022). In the soils, the shrink and swell processes generated micro-shearing and consequently the reorganization of the clay domains with the striated b-fabric formation (Mermut et al, 1988) which are micromorphological features specific to vertic materials (very rich in clay).…”

Mechanism of Potassium Release from Feldspar by Mechanical Activation in Presence of Additives at Ordinary Temperatures

“…Potassium feldspar has been widely studied as a potential potash fertilizer resource [ 6 , 7 , 8 ]. It may be alternated by water in some conditions [ 9 ] and used to produce multiphase slow-release fertilizers by sintering reaction [ 10 ].…”