Formation and occurrence of gemstones

Abstract

Most gemstones are minerals and stand out from other minerals by their beauty, durability and comparative rarity. These terms are to some extent flexible: diamond for example is very rare indeed compared to salt or quartz, but not compared to ruby, the particular conditions needed for the formation of which are encountered hardly at all. Few entirely new gem mineral species have been found in the last few years; tanzanite, appearing on the gem market in 1967, is a fine blue transparent variety of a mineral which had previously appeared in a totally different form with no gem potential whatever. It is not likely that many entirely new mineral species with gem application will now be found, although minerals already known occasionally turn up with new colours or optical effects such as asterism (star formation).