waste or slack in anthracite mining.

Physically, anthracite differs from ordinary bituminous coal by its
greater hardness, higher density, 1.3-1.4, and lustre, the latter being
often semi-metallic with a somewhat brownish reflection. It is also free
from included soft or fibrous notches and does not soil the fingers when
rubbed. Structurally it shows some alteration by the development of
secondary divisional planes and fissures so that the original
stratification lines are not always easily seen. The thermal
conductivity is also higher, a lump of anthracite feeling perceptibly
colder when held in the warm hand than a similar lump of bituminous coal
at the same temperature. The chemical composition of some typical
anthracites is given in the article COAL.

Anthracite may be considered to be a transition stage between ordinary
bituminous coal and graphite, produced by the more or less complete
elimination of the volatile constituents of the former; and it is found
most abundantly in areas that have been subjected to considerable
earth-movements, such as the flanks of great mountain ranges. The
largest and most important anthracite region, that of the north-eastern
portion of the Pennsylvania coal-field, is a good example of this; the
highly contorted strata of the Appalachian region produce anthracite
exclusively, while in the western portion of the same basin on the Ohio
and its tributaries, where the strata are undisturbed, free-burning and
coking coals, rich in volatile matter, prevail. In the same way the
anthracite region of South Wales is confined to the contorted portion
west of Swansea and Llanelly, the central and eastern portions
producing steam, coking and house coals.

Anthracites of newer, tertiary or cretaceous age, are found in the
Crow's Nest part of the Rocky Mountains in Canada, and at various points
in the Andes in Peru.

The principal use of anthracite is as a smokeless fuel. In the eastern
United States, it is largely employed as domestic fuel, usually in close
stoves or furnaces, as well as for steam purposes, since, unlike that
from South Wales, it does not decrepitate when heated, or at least not
to the same extent. For proper use, however, it is necessary that the
fuel should be supplied in pieces as nearly uniform in size as possible,
a condition that has led to the development of the breaker which is so
characteristic a feature in American anthracite mining (see COAL). The
large coal as ra