Geology Reference
In-Depth Information
Chapter 1
The Nature of Minerals and Rocks
as Materials
1.1 General
The classification, genesis, and geological role of the various minerals and rocks
are well covered in standard textbooks of mineralogy and petrology (Deer et al.
1992
; Mueller and Saxena
1977
; Best
2003
; Nesse
2000
; Perkins
2002
; Philpotts
and Ague
2009
; Vernon and Clarke
2008
; Wenk and Bulakh
2004
; Yardley
1989
).
Here we review briefly some of the characteristics of minerals and rocks that are
relevant from a materials science point of view. Minerals show a wide range in
physical and chemical properties, and rocks have the additional complexity of the
textural and structural variety of polycrystalline materials. However, there are
some generalizations that can be made. Thus, most minerals are electrically
insulating, optically transparent in thin sections, and brittle under ordinary atmo-
spheric conditions, and many are silicates in chemical constitution.
In the next two sections, we look at aspects of minerals and rocks that are of
particular relevance to their mechanical properties. In the case of minerals, this
involves the nature of the chemical bonding and of the defects in their crystal
structures. In the case of rocks, particular importance attaches to the nature of the
grain boundaries in intact rock and of pore structure in porous rock.
1.2 The Constitution of Minerals
1.2.1 Atomic Bonding
In their physical and chemical nature minerals cover a wide range. However,
comparing them with materials that are well studied because of technological
importance, they tend to be nearest to the oxides. The majority of rock-forming
minerals are, in fact, either oxides or oxy-salts, with the silicates forming the
