Mineral structures, defects and their evolution with pressure and temperature
The classic picture of mineral structures is dominated by the periodic repetition of the asymmetric unit over infinite distances. This picture is governed by the principles of symmetry and it has its merits for the description of bulk structures of minerals and their associated equilibrium properties.
However, apart from bulk structure, the properties of the actual mineral assemblies found in nature in the form of rocks are equally determined by mineral surfaces, grain boundaries and sub-grain microstructures. These diverse features require a description of minerals at very different length scales, ranging from the properties of atoms at the sub-ångström range (1 Å = 10−10 m), to the now fashionable nanometre range that would encompass a relatively small and still enumerable number of atoms in a world governed by the forces of quantum mechanics (Fig. 1).
Going on to the micrometre length scales of mineral microstructure and further to the length scales directly accessible to the human eye, i.e. millimetre grain sizes or rock deformations ranging from the metre to the kilometre range, the properties of these structures are more and more dictated by classical mechanics.
Any consideration of the composition, structure and properties of matter leads to the existence of atoms as its basic building units. Atoms may be approximated as spherical, with a diameter between 1 and 5 × 10−10 m. However, they are not indivisible (“ατομοσ”) as stated by Democritus, and modern physics of the past 100 years revealed the three fundamental particles protons, electrons, and neutrons.