Minerals and Gems

Abstract

We begin this chapter by explaining why we are including gems in a text on ceramics. Gems have been intimately linked with many developments in the use of ceramics or have been the motivation for what has become a leap forward in ceramic processing or application. We saw earlier how the efforts by August Verneuil in the early 1900s to produce synthetic ruby led to an industry that produces 2 × 10⁵ kg of single-crystal Verneuil sapphire each year. Similarly, flux-growth techniques and hydrothermal quartz owe much to the desire to create gems. Gemstones use some special properties of ceramics: they can be transparent but with a range of colors, they scatter light (the sparkle), and the valuable ones are generally very stable (the less valuable ones have often been treated); actually most gemstones have been processed in some way. We will discuss the well-known gems and a few of the lesser known gems (for their special features). The most important gems are diamond, ruby, sapphire, and emerald. However, many other gems that are less well known may often be more valuable. Incidentally, the weight of a gemstone is usually given in carats (5 ct = 1 g). We will also use this chapter to summarize the links between some preceding topics, including history. If a friend hands you a blue (or red, yellow, green, or colorless) faceted sparkling stone and asks you to identify it (because you studied ceramics) what do you do or say? So when you read this chapter, keep asking yourself—what ceramic science is involved here.