The idea that some gemstones are precious and others are only semi-precious is familiar to every buyer of colored stones. Precious stones -- diamond, ruby, sapphire and emerald -- traditionally command a premium price in the market due to their extraordinary color or brilliance and extreme rarity.

One common misconception is that the distinction between precious and semi-precious gemstones is traditional, going back many centuries. In fact it is a recent innovation, dating only to the nineteenth century. The first use of semiprecious to mean "of less commercial value than a precious stone" can be traced back only to 1858.

Another misconception is that the list of four precious gems has a long history. In fact the traditional list of precious gemstones is rather longer and includes some surprising members. Pearl, though not strictly speaking a gemstone, was considered to be precious; so was opal. But one of most the traditional precious stones with a history going back to ancient Greece was amethyst. Amethyst was reclassified as semi-precious after large deposits were found in Brazil and Uruguay in the first half of the nineteenth century. The introduction of the term semiprecious into the English lexicon corresponds to the new amethyst discoveries.

In the 19th century, world production of diamond was only a few pounds a year. After the discovery of the huge

The De Beers consortium also mounted a concerted decades-long advertising campaign to associate diamonds with love, courtship and marriage, under the now familiar slogan "Diamonds are Forever." The diamond engagement ring, once unknown in most parts of the world (including Europe), is now considered an essential part of the ritual of marriage. It is hard to avoid the conclusion that diamond's special position as a precious stone is due largely to monopoly economics and social engineering.