ange. He would
express his warm appreciation of the friendly spirit of cooperation and
advice with which this effort has been aided--a spirit which he likes to
think is particularly characteristic of the profession of economic
geology. In particular he would acknowledge the efficient aid of Mr.
Julian D. Conover in preparation and revision of the manuscript.

CHAPTER II

THE COMMON ELEMENTS, MINERALS, AND ROCKS OF THE EARTH AND THEIR ORIGINS

A list of the solid substances of the earth making up the so-called
lithosphere (or rock sphere) in order of their abundance, does not at
all correspond to a list made in order of commercial importance. Some of
the most valuable substances constitute such a small proportion of the
total mass of the lithosphere that they hardly figure at all in a table
of the common substances.

RELATIVE ABUNDANCE OF THE PRINCIPAL ELEMENTS OF THE LITHOSPHERE

When reduced to the simplest terms of elements the outer ten miles of
the lithosphere consists of:[1]

PERCENTAGE OF PRINCIPAL ELEMENTS IN THE LITHOSPHERE

Oxygen 47.33
Silicon 27.74
Aluminum 7.85
Iron 4.50
Calcium 3.47
Magnesium 2.24
Sodium 2.46
Potassium 2.46
-----
98.05

The remainder of the elements exist in quantities of less than 1 per
cent. None of these principal elements occur separately in nature and
none of them are mined as elements for economic purposes.

RELATIVE ABUNDANCE OF THE PRINCIPAL MINERALS OF THE LITHOSPHERE

Minerals exceptionally consist of single elements, but ordinarily are
combinations of two or more elements; for instance, quartz consists of a
chemical combination of silicon and oxygen. The proportions of the
common minerals in the outer ten miles of the lithosphere are in round
numbers as follows:

PERCENTAGE OF COMMON MINERALS IN LITHOSPHERE

Feldspar 49
Quartz 21
Augite, hornblende, and olivine 15
Mica 8
Magnetite 3
Titanite and ilmenite