Fig. 4: Leaching of feldspars and precepitation of secondary minerals in thermal experiments.

SEM images of the original K-feldspar grains used in the experiments (a), leached K-feldspar and authigenic minerals after the 14-d experiments (b–l). a surface of the original K-feldspar grains. b surface of the K-feldspar after experiment in the anhydrous n-C₂₀H₄₂ + feldspar system (II). c extensively leached feldspar (LF) in the C₂₀H₄₂ + H₂O + feldspar system (III). d extensively leached feldspar (LF) and euhedral boehmite (Bo) in the C₂₀H₄₂ + H₂O + feldspar system (III). e extensively leached feldspar (LF) in the C₂₀H₄₂ + D₂O + feldspar system (IV). f leached feldspar (LF) and euhedral kaolinite (Kao) in the C₂₀H₄₂ + D₂O + feldspar system (IV). g flower-like illite (muscovite) aggregates in the C₂₀H₄₂ + D₂¹⁸O + feldspar system (V). h lash-shaped boehmite in the C₂₀H₄₂ + D₂¹⁸O + feldspar system (V). i, j thin plate-shaped illite (muscovite) aggregates on the leached feldspar surface in the C₂₀D₄₂ + H₂O + feldspar system (VII). k subhedral plate-shaped illite (muscovite) on the leached feldspar surface in the C₂₀H₄₂ + H₂O + feldspar system (VIII). l small euhedral illite (muscovite) on the leached feldspar surface in the H₂O + feldspar system (IX). In the systems with only 20 mg feldspar, the feldspars were leached quite extensively (c–f), and secondary minerals, including kaolinite and illite, were precipitated on K-feldspar surfaces and were also detected in the water solutions. In the systems with 2 g feldspars, the feldspar grains were dissolved, and illite and muscovite precipitated on the K-feldspar surfaces (g–k) and were also detected in the water solutions.