Beauty from imperfections

Gemstones and minerals are attractive and coloured because they include impurities. The chapter discusses how such impurities are located in the crystal lattice structures, and the differences that ensue between natural and synthetic crystal growth. Whilst the latter may be controllable (e.g. for 30 cm long rubies) they are small compared with some natural mineral examples. Examples cited range from gemstones to lasers, but progress is only made once there is knowledge of the lattice locations of impurities in the host structure. This is often apparent from the crystallography and shape of natural minerals. Perfection (i.e. accurate and uniform placement of the impurities) is essential for laser crystals, whereas high value natural gemstones invariably show visible flaws. Understanding involves the role of chemistry, ionic sizes and thermal processing, in addition to the dopants.