Mining in Afghanistan "List of Goods Produced by Child Labor or Forced Labor" in which Afghanistan appeared to be one of the 74 countries with noticeable incidence of child labor in the coal mining field. Afghanistan is known to have exploited its precious and semi-precious gemstone deposits. These deposits include aquamarine, emerald and other varieties of beryl, fluorite, garnet, kunzite, ruby, sapphire, lapis lazuli, topaz, tourmaline, and varieties of quartz. Corundum deposits (sapphire and ruby) in the country are largely exhausted, and very little gem quality material is found. The four main gemstone-producing areas are those of Badakhshan, Jegdalek, Nuristan, and the Panjshir
History of manifolds and varieties History of manifolds and varieties The study of manifolds combines many important areas of mathematics: it generalizes concepts such as curves and surfaces as well as ideas from linear algebra and topology. Certain special classes of manifolds also have additional algebraic structure; they may behave like groups, for instance. In that case, they are called Lie Groups. Alternatively, they may be described by polynomial equations, in which case they are called algebraic varieties, and if they additionally carry a group structure, they are called algebraic groups. The term "manifold" comes from German "Mannigfaltigkeit," by Riemann. In English, "manifold" refers to