STANDING TALL: PLAINS INDIANS ENJOYED HEIGHT, HEALTH ADVANTAGE. COLUMBUS, Ohio - Equestrian Indian tribes on the American Plains in the late 1800s were the tallest people in the world, suggesting that they were surprisingly well-nourished given disease and their lifestyle, a new study found.
Limestone often contains variable amounts of silica in the form of chert (chalcedony, flint, jasper, etc.) or siliceous skeletal fragment (sponge spicules, diatoms, radiolarians), and varying amounts of clay, silt and sand (terrestrial detritus) carried in by rivers.
Silica, also known as silicon dioxide, is a compound made out of the two most abundant elements in the Earth's crust, silicon and oxygen (SiO2). Silicon is not found free in nature but occurs chiefly as silica. Silicon is important to plant and animal life.Silicon was recognized as an essential trace element is 1972.hemistry: Silica, also known as silicon dioxide, is a compound made out of the two most abundant elements in the Earth's crust, silicon and oxygen (SiO2). Silica has three main crystalline varieties: quartz (by far the most abundant), tridymite, and cristobalite.