It was De Beers, the diamond company, that came up with advertising campaigns that convinced us to buy diamonds. Diamonds are Forever and all that. Ultimately, unless you have a large flawless diamond, the resale value is not good. Rings with lots of tiny diamonds bought at a chain store are often worth a fraction of what you pay. Appraisal value is also overinflated, and insurance companies never offer much to replace a diamond (unless the colour, clarity and carat weight is very very good).
Birthstone rings were more common in previous years, as were acrostic rings. This ring, for example, spells out DEAREST (diamond, emerald, amethyst, ruby, emerald, sapphire tourmaline). From Wikipedia:
This one spells Regards (Ruby, emerald, garnet, amethyst, diamond, sapphire). Source
