Selenite (mineral) was filled with mineral-rich water that drove the crystals' growth. The largest of those crystals weighs 55 tons, is long, and is over 500,000 years old. Gypsum occurs on every continent and is the most common of all the sulfate minerals. Gypsum is formed as an evaporative mineral, frequently found in alkaline lake muds, clay beds, evaporated seas, salt flats, salt springs, and caves. It is frequently found in conjunction with other minerals such as, copper ores, sulfur and sulfides, silver, iron ores, coal, calcite, dolomite, limestone, and opal. Gypsum has been dated to almost every geologic age since the
Vegetation influential, clear and simple classification scheme for types of vegetation was produced by Wagner & von Sydow (1888). Other important works with a physiognomic approach includes Grisebach (1872), Warming (1895, 1909), Schimper (1898), Tansley and Chipp (1926), Rübel (1930), Burtt Davy (1938), Beard (1944, 1955), André Aubréville (1956, 1957), Trochain (1955, 1957), Küchler (1967), Ellenberg and Mueller-Dombois (1967) (see vegetation classification). There are many approaches for the classification of vegetation (physiognomy, flora, ecology, etc.). Much of the work on vegetation classification comes from European and North American ecologists, and they have fundamentally different approaches. In North America, vegetation types are