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Accurately dating phenocrysts in Holocene volcanic rocks poses many challenges but is critical to placing magmatic processes that occur prior to eruption into a temporal frame-work. We dated alkali feldspar (i.e., orthoclase Or₁₀ to Or₄₆) crystals in four young phonolites from the Teide–Pico Viejo volcanic complex, Tenerife (Spain), using (²²⁶Ra)/(²³⁰Th) isotopes. Partition coefficients of Ra (D_Ra) and D_Ra/D_Ba of feldspars were predicted using an approach based on the lattice strain model, which yielded crystallization ages that overlap or predate known eruption ages for the Lavas Negras (ca. 1 ka), Montaña Blanca (ca. 2 ka), Arenas Blancas (ca. 2–4 ka), and Teide H (ca. 6 ka) phonolites. Crystallization of feldspar may occur up to the time of eruption, with >8 ka crystals also present, possibly suggesting extended magma differentiation times. However, feldspars yielding finite (²²⁶Ra)/(²³⁰Th) ages are …