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.
Best Answer: Intermediate rocks contain between 53% and 65% silica. They also contain potassium and plagioclase feldspar with a small amount of quartz.est Answer: Intermediate rocks contain between 53% and 65% silica. They also contain potassium and plagioclase feldspar with a small amount of quartz.