High Quality Content by WIKIPEDIA articles! Greensand or Green sand is either a sand or sandstone, which has a greenish color. This term is specifically applied to shallow marine sediment, that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay minerals,such as smectite and glauconite mica. Greensand is also loosely applied to any glauconitic sediment.