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The ¹⁸O/¹⁶O of precipitated silica in natural environments is posited to record the temperature of the ambient environment. Measurements of ¹⁷O/¹⁶O in silica (SiO₂), when paired with ¹⁸O/¹⁶O, provide an opportunity to further constrain the environmental conditions at the time of mineral precipitation and ripening. On Cenozoic timescales, siliceous frustule precipitation by diatoms has served as the primary sink of silica from the ocean. Frustule precipitation is a biologically catalyzed process from an ocean undersaturated in SiO₂. Here, we measure the ¹⁷O/¹⁶O and ¹⁸O/¹⁶O in diatom frustules from semicontinuous cultures with two different diatom species and across a range of growth rates and temperatures. To further enable these measurements, we developed a laser fluorination method to reproducibly measure the triple oxygen isotope composition of silica frustules. While the δ¹³C of the organic matter …