CHAPTER III.. Rock-and Soil-Forming Minerals, 29.—Quartz, Quartzite,

ROCK-AND SOIL-FORMING MINERALS, 29.—Quartz, quartzite, jasper, hornstone, flint, 29.—Solubility of silica in water; absorption by plants, 30.—Silicate Minerals, 31.—Feldspars, their Kaolinization, 31.—Formation of Clays, 33.—Hornblende or Amphibole, Pyroxene or Augite, 33.—Their Weathering and its Products, 33.—Mica, Muscovite and Biotite, 35.—Hydromica, Chlorite, 35.—Talc and Serpentine; “Soapstone”, 36. The Zeolites; Exchange of Bases in Solutions, 36.—Importance in Soils, in Rocks, 38.—Calcite, Marble, Limestones; their Origin, 39.—Impure Limestones as Soil-Formers, 40.—Caves, Sinkholes, Stalactites, Tufa, 41.—Dolomite; Magnesian Limestones as Soil-Formers, 42.—Selenite, Gypsum, Land Plaster; Agricultural Uses, 42.—Iron Spar, Limonite, Hematite, Magnetite, 44.—Reduction of Ferric Hydrate in Ill-drained Soils, 45.