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Coals contain both organic and inorganic phases. The latter consist either of minerals such as quartz and clays that may have been brought in by flowing water (or wind activity) or of minerals such as pyrite and marcasite that formed in place (authigenic). Some formed in living plant tissues, and others formed later during peat formation or coalification. Some pyrite (and marcasite) is present in micrometre-sized spheroids called framboids (named for their raspberry-like shape) that formed quite early. Framboids are very difficult to remove by conventional coal-cleaning processes. By analogy to the term mineral, British botanist Marie C. Stopes proposed ...(100 of 6066 words)