loss of the molecular hydrogen (H₂) byproduct. The reaction can be further facilitated by dissolved carbon dioxide (CO₂) and sulfur dioxide (SO₂), which lower the pH of brine films increasing the concentration of the more oxidative hydrogen ions (H⁺).

However, higher temperatures (c. 300 °C) are usually needed to decompose Fe³⁺ (oxy)hydroxides such as goethite into hematite. The formation of palagonitic tephra on the upper slopes of the Mauna Kea volcano may mirror such processes,