Fig. 1. Cumulative B extracted as a function of sequential extractions (12 h, 1:10 w/v with 0.1 M CaCl₂ for the first three extractions and 0.01 M CaCl₂ for subsequent extractions). The specific surface areas were as follows: Twisselman clay loam (<250 µm), 31 m² g^–1; Traver silt loam (<250 µm), 27 m² g^–1; Morris illite (<50 µm), 62 m² g^–1; Weathered serpentine (<50 µm), 38 m² g^–1; Fithian illite (<50 µm), 52 m² g^–1; Fresh serpentine (<50 µm), 18 m² g^–1; Moreno Gulch shale (<250 µm), 30 m² g^–1; and Salt Creek shale (<250 µm), 75 m² g^–1.