THE SCOPE OF ECONOMIC GEOLOGY 3
of geology known as petrology. Leading British mineralo-
gical authorities define minerals as inorganic materials.
The British Museum (Introduction to Study of Minerals,
PP. 1-2) adopts as mineral ‘the unorganized products of
our own Earth ” and of outer space, including soil and rock.
Sir Henry Miers (Mineralogy, 1902, p. I) defines as mineral
“ the materials which constitute the solid crust of the earth,
and refers to granite and coal as minerals, Coal, petroleum,
slate, and ironstone are not ** mineral species; but they are
minerals according to legal and commercial usage, and to
leading mineralogists, The definition which asserts that
most branches of the mining industry and of economic
mineralogy are not concerned with minerals is more para-
doxical than sagacious.!
ORE-GRADE—The student of economic geology has to
consider the commercial value of minerals, which depends
on many factors, including accessibility to a market, the cost
of working, the price of the usefyl constituent, and its
chemical condition, and the grade of the ore. Deposits
containing large supplies of useful mineral in positions re-
mote from markets may be useless owing to the cost of trans-
port. A material containing less than 1 per cent. of copper
may be valuable if the copper be native, but not if it be a
sulphide that would require smelting. An iron ore may be
worthless if it contain less than 50 per cent. of iron ; whereas
an ore may be valuable with 1 part of platinum in 100,000
parts, and alluvial beds have paid to work that yielded 1 part
of gold to 15 million parts of dross. Price has therefore to
be considered in connection with all economic minerals.
Hence in the chapters dealing with ores, facts are stated as
to the range of price of the metals,
MeTaL—The term metal is not used in economic geology
in its chemical sense, but with the general meaning of opaque
substances which have a bright lustre, can be melted, and
are usually heavy. Calcium, sodium, and potassium, which
are metals according to chemical terminology, are regarded
by the economic geologist as non-metallic, He regards
most ores as consisting of metallic and earthv constituents.
L For further definitions see “What is a Mineral? * 7%. IME,
1909, vol. xxxvii, pp. 13-42.
