[little jeremiah]

It is interesting. I’ve read that diamonds are actually quite common and the only reason the price is high is DeBeers owning so many mines and restricting the number of diamons for sale.

[defconw]

Follow the money! :) You are right over that target.

[Richard Kimball]

Yes. Diamonds did not used to be a particularly valuable gem. Rubies, emeralds, etc, were all more valued. A small group of individuals cornered the market, and it was followed with a media campaign to make diamonds the most valuable gem.

Check out this musical number from Gentlemen Prefer Blondes:

Diamonds Are a Girl's Best Friend

Look at it not as a musical number, but as an advertisement. The studio owners were also involved in the diamond cartel.

DeBeers was the company that convinced people engagement rings HAD to be diamonds, and this was their "rule of thumb" for how much you should spend on one:

General Rule: You should spend at least 2 months salary on the engagement ring. If, for example, you are making $60,000 per year, you should spend $10,000 on the engagement ring.