ommon rocks is used commercially in crushed
or comminuted forms for road material, for railroad ballast, and for
cement, brick, concrete, and flux. In blocks and structural shapes, of
less aggregate tonnage, they are used as building stone, monumental
stone, paving blocks, curbing, flagging, roofing, refractory stone, and
for many other building and manufacturing purposes.

The common rocks are commodities in which most countries of the globe
are self-sufficing. International trade in these commodities is
insignificant, being confined to small quantities of materials for
special purposes, or to local movements of short distances, allowed by
good transportation facilities.

The common rocks are so abundant and widespread that the conservation
of raw materials is not ordinarily a vital problem. Conservational
principles do apply, however, to the human energy factor required for
their efficient use. In the valuation of common rocks, also, the more
important factors are not the intrinsic qualities of the stones, but
rather the conditions of their availability for use.

Because of bulk and comparatively low intrinsic value, the principal
commercial factors in the availability of the common rocks are
transportation and ease of quarrying, but these are by no means the only
factors determining availability. Their mineral and chemical
composition, their texture and structure, their durability, their
behavior under pressure and temperature changes, and other factors enter
in to important degrees. The weighting and integration of these factors,
for the purpose of reaching conclusions as to the availability of
particular rock materials, depend also on the purposes for which these
materials are to be used. The problem is anything but simple. The search
for a particular rock to meet a certain demand within certain limits of
cost is often a long and arduous one. On account of the abundance and
widespread distribution of common rocks and their variety of uses, there
is a good deal of popular misapprehension as to their availability. Many
building and manufacturing enterprises have met disastrous checks,
because of a tendency to assume availability of stone without making the
fullest technical investigation. Many quarrying ventures have come to
grief for the same reason. It is easy to assume that, because a granite
in a certain locality is profitably quarried and used, some other
granite in the same locality has equal chances. However