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.
The vast majority of minerals in the Earth's rocks, from the crust down to the iron core, are chemically classed as silicates. The silicate minerals are all based upon a chemical unit called the silica tetrahedron.The silica tetrahedron consists of a silicon atom surrounded by four oxygen atoms.solated silica tetrahedra occur in many silicates such as olivine, where the tetrahedra are surrounded by iron and magnesium cations. Pairs of tetrahedra (SiO 7) occur in several silicates, the best known of which is probably hemimorphite.