<p>Since Bernal’s 1949 Guthrie Lecture, clays have been invoked as central actors in prebiotic chemistry experiments. Landmark experiments with montmorillonite (MMT) showed oligomerization of activated ribonucleotides in water, elevating clays to a putative universal solution for RNA assembly. Here, we argue that current evidence supports a more nuanced framing: clays should be considered explicit experimental variables, not passive or uniform catalysts, but tunable parameters whose effects depend on well-defined conditions. Mineral identity, activation state, solution chemistry, and cycling history jointly determine whether surfaces concentrate and organize RNA, assist condensation under specific regimes, or accelerate backbone hydrolysis. Early Earth plausibility also points beyond Na-MMT to Fe-rich smectites and silicate glasses. Adopting a “parameter, not panacea” framework improves reproducibility, invites direct tests across realistic mineral panels, and situates clays within a broader geochemical toolkit that includes wet-dry cycles and rock glasses.</p>