Rocks that have cooled more slowly have time to build stronger bonds, so they are more resistant to the forces of weathering. Friedrich Mohs, an Austrian mineralogist, devised a scale of mineral hardness in 1812. He used ten minerals, listed below, as standards by which to determine the hardness of minerals and other objects. These ten minerals were arranged on a scale of increasing hardness. For instance, gypsum can scratch talc, and apatite can scratch fluorite, calcite, gypsum, and talc.
Diamonds are the hardest mineral in existence and are used as cutting instruments.
Also published by Alfred A. Knopf, Inc., New York. Since some minerals weather more rapidly than others and weathering processes vary in intensity and combination, weathering products contain different mineral combinations. Pedologists , or soil scientists, classify these weathered mineral products as soil separates . An Introduction to Physical Geography, by Robert W. Christopherson,MacMillian College Publishing Company, New York.