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The element mercury (Hg) can develop large mass‐independent fractionation (MIF) (Δ199Hg) due to photo‐chemical reactions at Earth's surface. This results in globally negative Δ199Hg for terrestrial sub‐aerially‐derived materials and positive Δ199Hg for sub‐aqueously‐derived marine sediments. The mantle composition least affected by crustal recycling is estimated from high‐3He/4He lavas from Samoa and Iceland, providing an average of Δ199Hg = 0.00 ± 0.10, Δ201Hg = −0.02 ± 0.0.09, δ202Hg = −1.7 ± 1.2; 2SD, N = 11. By comparison, a HIMU‐type lava from Tubuai exhibits positive Δ199Hg, consistent with altered oceanic crust in its mantle source. A Samoan (EM2) lava has negative Δ199Hg reflecting incorporation of continental crust materials into its source. Three Pitcairn lavas exhibit positive Δ199Hg which correlate with 87Sr/86Sr, consistent with variable proportions of continental (low Δ199Hg and high 87Sr/86Sr) and oceanic (high Δ199Hg and low 87Sr/86Sr) crustal material in their mantle sources. These observations indicate that MIF signatures offer a powerful tool for examining atmosphere‐deep Earth interactions. Plain Language Summary: While Earth's mantle is continuously chemically and isotopically stirred by convection, some ocean island lavas preserve isotopic anomalies. Their most likely origin is the recycling of crustal material into Earth's mantle by subduction. A question is then whether these crustal materials originate from the ocean or the continents. By using mercury stable isotopic compositions, which have specific signatures in ocean and continent materials, we identify whether these anomalies are due to continental or oceanic crustal material in various ocean island basalts. Key Points: The Hg isotopic composition of the primitive mantle was determined by analyzing lavas from the Samoa and Iceland hotspotsKey samples from the canonical mantle end member were analyzed to track crustal recycling in the mantleWe demonstrate the presence of recycled oceanic and continental materials in the source of ocean island basalts [ABSTRACT FROM AUTHOR]