Brown Coal, one of the three great families into which coals are divided by mineralogists, and which are again subdivided into many subordinate varieties. In England it is also called Bovey coal, from Bovey, near Exeter, where it is principally found. The German deposits of brown coal are mainly in Prussian Hesse, Thuringia, the valley of the Rhine, the Wester-wald (a hill chain in northern Nassau), and in Saxony. The mineral is also found in Alsace. Vegetable matters are met with in various stages of their conversion into mineral coal. In the formations of the present period they are found in great collections of peat, which are sometimes seen in beds alternating with others of sand and of clay. In the tertiary strata these vegetable collections occur in beds interstratified with others of limestone and the various rocks of this period. In some instances the plants are little altered, so that the species' are easily recognized by the structure of the leaves and fruit. The stems are flattened and cross each other in all directions. The woody fibre has become more or less impregnated with bitumen, so that it burns with the peculiar smoke and flame of that substance. This material is called lignite, and sometimes brown coal.
Beds of it are worked for fuel in upper Hesse. Another variety of brown coal is more altered in structure, so that its vegetable character is more indistinct, the beds presenting stratified bodies of dark, nearly black substance, with an earthy fracture. The lignite is sometimes seen mixed in the same specimen. This variety of brown coal is worked in the vicinity of Cassel. These varieties make but a poor quality of fuel, often containing from 30 to 48 per cent, of water. A large proportion of this, however, may be expelled by drying, though even then 8 per cent, or more may be reabsorbed. The amount of ash varies in the different qualities from less than 1 to more than 50 per cent. Sulphates of lime, potash, and iron often occur as impurities, and nitrogen is sometimes met with to the extent of 15 per cent. In 21 different analyses of brown coal by different chemists, the proportion of carbon is found to vary from 50 to 70 per cent. Brown coal has been found on both sides of the Andes in South America, and in numerous deposits on the eastern and western slopes of the Rocky mountains. - Jet is a black variety of brown coal, compact in texture, and taking a good polish, whence its use in jewelry.
The oil extracted from brown coal, oleum ligni fossilis, is used for medicinal purposes. (See Coal).