Tigriopus californicus ingest sediment at a rate dependent on the suspension concentration and on particle mineralogy. Ingested minerals undergo chemical and mineralogical transformation that depend on initial mineralogy and residence time in the digestive tract. Clinochlore altered to Mg-chamosite with a reduction in Mg and an increase in Fe. Tremolite partially altered to chamosite with a reduction in both Mg and Ca. Montmorillonite altered to vermiculite and mica with an increase in Mg, Ca, and Fe. Gypsum formed in some mineral-bearing pellets. Such chemical changes may in part explain alteration of minerals in the marine environment. Ingested clays are mostly in the form of flocs. Planktonic pellets settle through the water column much faster than the settling of their component particles. The increased settling rate allows clay-size particles to be deposited where the hydrodynamic conditions suggest only coarse silt and fine sand should occur.