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name of brown coal "those fossil accumulations of the more or less carbonized remains of plants which occur in the Tertiary formation."
Under this classification "Lignite" is made the name of a variety of brown coal, and is not used as a generic term.
Brown coal, whether considered physically or chemically, may be justly regarded as a substance intermediate between peat on the one hand and bituminous coal on the other. There is no hard and fast line of division between these substances, but each grades into the other by such small differences that it can not be said where one ends and the other begins. Indeed, so closely do certain varieties of each simulate the other, that there is no test which can decide between them as to which is bituminous coal and which is brown coal, and the determination can only be made by their geological relations.
Zincken says of this:
"There are no physical or chemical qualities by means of which a coal may in every instance be characterized as a brown coal and distinguished from the other species of coal. Coals of different formations are in their external character similarly variable. At Malowka, in Russia, a Carboniferous coal has been found, which possesses altogether the appearance of a brown coal, and one of the more recent ones at that. The fact of its relative position as belonging to the Carboniferous formation, was first determined only after careful scientific investigation. There are Cretaceous coals which appear to be identical with certain kinds of brown coal, and alluvial coals, even peat itself, are met with, which closely resemble varieties of stone coal. Hence, the only certain method of determining the relative age of a coal is by the geological and paleontological conditions of its occurrence."
ORIGIN.
The fossil fuels are mainly of vegetable origin, and their differences are principally due to the character of the vegetation from which they "
"Brown coal or lignite contains 20-30 per cent of oxygen after the expulsion at 100 degrees C. of 15-36 per cent of water [as against "5-15 per cent (rarely 16-17) of oxygen, ash excluded," in ordinary bituminous coal]. The hydrogen in each is 4-7 per cent. Both have usually a bright pitchy luster (whence often called Pechkohle in German), a firm, compact texture, are rather fragile compared with anthracite, and have a specific gravity from 1.14 to 1.40. The brown coals have often a brownish-black color, whence the name, and more oxygen, but in these respects and others they shade into ordinary bituminous coals." —Dana, J. D., System of Mineralogy, 1892, p. 1021.
Zincken, C. F. Die Physiographie der Braunkohle, Leipzig, 1867, p. 5.