Duero River, Tudera de Duero, Valladolid, Spain

It is fine sand (0.1-0.3mm in diameter) mixed with coarse sand (1-3.0mm in diameter).  The fine sand consists of quartz, and coarse sand consists of well-rounded grains of quartz, chert, quartzite, weathered sandstone and so on.  Small quantity of silt was included before washing.