328 DESCRIPTIONS OF MINERALS. 
low flame, and has hence been used as candles—whence the 
name. It affords when heated a large amount of mineral 
oil, and may be used for its production. The volatile in- 
gredients sometimes amount to 50. or 60 per cent. It is 
often made into inkstands, snuff-boxes, and other: similar 
articles. 
4. Brown Coal usually has a brownish-black color, and 
contains 15 to 20 per cent. of oxygen, but much resembles 
in appearance bituminous coal. ‘he term brown coal is ap- 
pled generally to any coal more recent in origin than the 
era of the great coal beds of the world. The name lignite 
has sometimes the same general application, though without 
strict propriety. Lignite is the part of brown coal which 
has the woody structure still apparent. 
Jet resembles cannel coal, butis harder, of a deeper black 
color, and has a much higher lustre. It receives a brilliant 
polish, and is set in jewelry. It is the Gagates of Diosco- 
rides and Pliny, a name derived from the river Gagas, in 
Syria, near the mouth of which it was found, and the origin 
of the term jet now in use. 
Native Coke vesembles somewhat artificial coe, but is 
more compact, and some varieties of it afford a consider- 
able amount of bitumen. It occurs at the Mdgehill mines 
near Richmond, Virginia, according to Genth, who attri- 
butes its origin to the action of a trap eruption on bitumi- 
nous coal. | | 
It is now well established that mineral coal is mainly of 
vegetable origin, and that the accumulations out of which 
the coal beds were made were very similar in character, 
though not in kinds of plants, to the peat beds of the pres- 
ent day. Peat is vegetation which has undergone, in part, 
the change to coal; and in some cases 1t has become brown 
coal. The conditions of change are somewhat different from 
those of the beds of good coal, since, in the case of the peat, 
the air has access, while in that of the coal the air was more 
or less excluded by overlying strata; and the more perfect 
the exclusion, other things equal, the better the coal. As 
the composition of mineral coal is closely related to that of 
mineral oils, the explanation of the origin of the latter, given 
on page 323, suffices to illustrate also the origin of the 
former. With a less complete exclusion of the air, oxygen- 
ated hydrocarbon compounds, like coal, would be a natural 
result. 
