Several years ago the term "urban mining" took off. It referred to the discovery of precious metals that were "buried" in people's homes in the form of personal possessions like jewelry and home electronics that they weren't using. A lot of cell phones, for instance, use gold and other valuable materials in their circuits, and when the price of these substances was high, brokers would pay premium prices for them, no matter where they came from or what form they were in.

At the time, gems were not coveted so much, but that's changed. Right now, the price of diamonds on the world market is about 30 percent higher than it was a year ago, according to a recent article in Chunichi Shimbun, thanks to a healthier world economy. Consequently, well-to-do people in Asia, North America and the Middle East are craving diamonds, and foreign buyers, particularly from the U.S., China, India and Dubai, are flocking to Japan because they think there are a lot of the rocks here "sleeping" in people's closets and vanity cases.

The reason is simple. During the bubble period of the late '80s, when the value of various assets was higher than it probably should have been, people with even a little money bought a lot of jewelry that they don't wear any more. Many of these people probably have forgotten they even have diamonds.