Silicate minerals rapidly release silica to sea water. Fine-grained, 1-gram samples were placed in 200 milliliters of sea water, and the silica content of the water was measured intermittently for 6 months. At the end of 10 days and of 6 months the silica concentrations with various minerals, in parts per million, were, respectively: kaolinite, 0.6, 2.2; chlorite, 2.5, 2.4; illite, 1.8, 2.6; muscovite, 1.8, 3.9; montmorillonite A, 7, 10.5; montmorillonite B, 10, 21. Except for ion exchange phenomena, it generally has been assumed that these minerals do not react significantly with sea water, or, if they do, they react at geologically slow rates. The rates observed indicate that the ocean must be looked upon as a chemical system with a rapid response to added detrital silicates.