Real‐Time Observations and Etching Rates of Quartz and Feldspar

ABSTRACT Mineral grains extracted from sediment, such as quartz and feldspar, are routinely etched with hydrofluoric acid (HF) at concentrations of either 40% or 10% for various durations. This treatment serves two main purposes: removal of nonfeldspar constituents and removal of the outer surface layer. This study presents the real‐time analysis of HF etching using a novel experimental setup designed for this purpose. Our study provides new insights into the etching mechanics and reveals significant inhomogeneities in individual grains. We quantitatively monitored the etching of 150‐ to 300‐μm K‐feldspar (in 10% and 40% HF), as well as polymineralic and quartz grains (in 40% HF), for durations ranging from 2 to approximately 9 h. Based on a statistical assessment of 17 quartz grains, we report a median etching rate of 5.96 μm·h −1 with a Q1–Q3 range of 3.96–7.55 μm·h −1 for quartz in 40% HF solution and 25.5 μm·h −1 for K‐feldspar in 10% HF solution. Additionally, we report an overall increase in transparency, as nontransparent grains are more easily fragmented due to their structure. Our results reveal two key findings: first, the etching process is highly inhomogeneous across the surface of individual grains; second, etching rates are variable and somewhat lower than reported in previous studies. This work provides the first direct evidence of the inhomogeneous dynamics of HF etching, offering crucial implications for the accuracy and reproducibility of trapped charge dating methods. For quartz, our measured etching rates are considerably lower than the commonly assumed values, indicating a likely systematic error of approximately 2%. This error consequently influences calculated luminescence ages.