THEO. F. BROOKINS, B. S., Principal Au Sable Forks Union Free School
and Academy, New York.
Among minerals of economic importance carbon minerals hold the unique
position of being at the same time of the most common and the most rare
occurrence. As far as external appearance indicates, a piece of common
coal and the most brilliant diamond are widely separated; with regard
to chemical composition they are closely related. Intermediate between
the coal of the stoke furnace and the "brilliant" of the jewelry
shop is still another well-known form of carbon, the graphite of the
lead pencil. These three substances comprise the far greater part of
carbon-containing minerals.
In so far as our mind's picture of a mineral is that of an aggregation
of crystals of fairly perfect form our consideration of coal as a
mineral is erroneous. We must yield to a broader interpretation of the
essential characteristics of a mineral and modify our idea so as to
include any homogeneous substance (solid, with the single exception of
mercury) of fairly definite chemical composition "occurring in nature
but not of apparent organic origin." Organic substances are those that
are alive or have lived.
Vegetation is, undoubtedly, the origin of all coal, but often much more
than a cursory examination is necessary to prove such origin. In the
less altered coals the vegetable origin is readily proved by the actual
presence of seeds, plant fibers, and other equally apparent organic
remains. A microscopic study is necessary for finding the presence
of woody fiber in the more metamorphosed form. The word metamorphose
comes from the Greek; _meta_ means after or over; _morphe_ is form. A
metamorphosis is a change of form or a forming over.
The history of the discovery of the value of coal as a means of
producing heat and of the development of the coal-mining industry
covers a comparatively recent period. Coal occurs in such quantities
near the surface of the earth's crust and its outcrops are so numerous
that it cannot have failed to attract the attention of the most ancient
of peoples. Indeed, that coal could be used as a fuel is mentioned by
a writer, Theophrastus, who lived 300 years B. C. The ancient Celts of
Britain are reputed to have evidenced knowledge of the industrial value
of coal. It was not until near the middle of the thirteenth century,
however, that coal became so important an economic product as to result
in statutes granting to certain places the privilege of mining it.
After a long period of trial in England the superiority of coal over
other fuels was recognized, and stone coal, as the harder form was
commonly known, came into general use. In America bituminous, or soft
coal, was mined to a slight extent in the latter half of the eighteenth
century. The form now commonly used in house-heating furnaces,
anthracite, for a long time baffled the colonists in their efforts to
make it burn. The knowledge that an anthracite fire is most effective
if not continually poked is said to have been acquired generally by
accident.
Europe and the United States to-day produce practically all the coal of
the world. In Europe, Great Britain, Germany, France, Austria-Hungary,
and Belgium are the main sources of supply. Several important coal
areas exist in our own country, notably that of the New England basin,
with an area of 500 square miles; the Appalachian district, with an
area of 65,000 square miles; the northern area, in Michigan, covering
7,000 square miles; the central area, comprising parts of Illinois,
Indiana and Kentucky, and including 48,000 square miles; the scattered
western area, with a total of 98,000 square miles; the indefinite
Rocky Mountain area, and the Pacific coast region, including parts of
California, Oregon, and Washington. Coal mining is yet an undeveloped
industry in our territorial possessions. Alaska has an abundant supply
of coal, and lesser quantities are found in Cuba and Porto Rico.
Mention has already been made of the two common kinds of coal,
bituminous and anthracite. These two kinds mark different stages in
the transformation from plant organism to mineral product. As the
biologist traces the successive steps in the evolution of an individual
of a species from germ to adult, so the geologist unfolds before us
the wonderful history of a piece of coal from its first appearance
on the earth to the time when it is thrown into our fire grate as
fuel. Coal is the metamorphosed product of vegetable growths, changed
by atmospheric agencies and the internal forces of the earth acting
through a total period of perhaps millions of years. In the remote
past, ages before man had appeared on the earth, the atmosphere or our
globe was highly charged with carbon gases. Vegetation flourished in
luxuriance. Great swamps were common. The ocean alternately covered
and receded from verdure-clothed land areas. Ponds were transformed
to morasses and swamps. In the swamps thus formed, the accumulated
sediment of centuries upon centuries covered alternate layers of
decayed plant organisms, until finally beds of peat were formed.
Great masses above pressed on those underneath; the internal heat of
the earth reached up and transformed the densely packed masses of
peat until the beds became hard and brown, the product of the partial
metamorphism being what we know as lignite, or brown coal. With the
continued action of the forces of metamorphism, the lignite turned
still darker, and as more gases were driven off, became heavier, until
the bituminous stage was reached, which, in turn, was succeeded by the
anthracite stage.
Graphite, or black lead, is a mineral containing not more than five
per cent of impurities, and is generally supposed to have originated
as did mineral coal, and to represent a still more advanced stage of
development. It occurs in various localities both in the vicinity of
coal measures and far removed from them. The chief part of the world's
supply comes from Ceylon, though Germany and the United States produce
quantities of graphite of excellent quality. In the Laurentian rocks of
Canada, and of course with as ancient origin, extensive deposits are
found. This presence of graphite in strata in which as yet no certain
traces of organic life have been found has led some to believe that
this form of carbon mineral may have another than organic origin.
Various uses are served by graphite. The chemist finds it of great
value in making his crucibles; the engineer uses it, finely powdered,
as a lubricant; the housekeeper polishes stoves with it; the
electrician uses it in his arc lights; all civilized nations use it
in the lead of lead pencils. The stem, _grapho_ (to write), on which
so many of our words, as geography, telegraph, graphophone, etc., are
formed, suggests also the origin of the name, graphite. The finest
quality lead pencils are those made from graphite occurring in a state
sufficiently pure to allow the cutting and grinding of pieces to the
size needed. In the case of the medium and poorer grade pencils, the
graphite has first been finely powdered and then pressed into the
requisite shape and size.
The purest form of carbon found in nature is the diamond. The rare
occurrence of diamonds indicates that the essential conditions in
nature for causing the transformation of some less pure form of
carbon into diamond are seldom present. While diamonds have actually
been produced in the laboratory by far-seeing and indefatigable
chemists, yet the cost of such products is so great as to preclude the
possibility of the most precious of gems becoming at all common. The
diamond is the hardest of all known substances, and will scratch any
other mineral across which it may be drawn.
Three localities have successively furnished the main part of the
world's stock of diamonds. A century and a half ago, practically all
the diamonds came from India, where at one time 60,000 persons were
employed in diamond digging. Toward the middle of the eighteenth
century, when the diamondiferous districts of India were becoming
exhausted, the discovery of the precious gem in Brazilian deposits
was made. At present, the supply of diamonds from Brazil has much
diminished, and the diamond fields of South Africa, where is located
the famous Kimberley mine, produce the larger part of the world's
output of diamonds.
Among famous diamonds of the world should be mentioned the Koh-i-noor
of the British crown, which, Hindu legend relates, was worn five
thousand years ago by one of their national heroes. The largest known
diamond, weighing three hundred sixty-seven carats, was found in
Borneo, and is now owned by the Rajah of Matan.