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.