What is each piece of sand called?

Each piece of sand is called a grain of sand, and that is the standard scientific and everyday term. Geologists refer to individual particles as sand grains or sand particles. If you want to be more specific by composition, a grain of sand can be called a quartz grain if it is made of quartz, a feldspar grain, a shell fragment, a coral fragment, or a mineral grain depending on what it is made of. In sedimentology, each grain is also classified by size, such as very fine sand grain, fine sand grain, medium sand grain, and coarse sand grain. Under a microscope, each grain has its own shape and is described as rounded, sub-rounded, angular, or sub-angular. In poetic or literary language, people sometimes call a single grain a speck of sand, a fleck of sand, or a particle of sand. The phrase grain of sand is famous in literature and philosophy to illustrate vast numbers and the smallness of individual things, as in the number of grains of sand on all the beaches. So while sand as a bulk material is uncountable, one piece is always called a grain of sand, and a handful is called sand grains.