It’s a story that sounds straight out of Hollywood: professional thieves disguised as police officers, big guns, an airplane about to take off, and $50 million in diamonds — stolen. But the thieves are unlikely to walk away with all that money. By some estimates, they’ll get about 20 percent of the value when they resell the stones.

That number got us thinking about our own diamonds sparkling on our fingers. Just how much are they actually worth if we wanted to sell them?

Probably not as much as you might think.

Jeweler Sam Chamsi has been selling diamonds in Los Angeles’ jewelry district for nearly 25 years. In all that time, he says, he’s only had a couple of gents (and their diamond engagement rings) get rejected by their chosen ladies. And when they do, he tries to return as much of their money as he can. The first time it happened, he said, he gave it all back. The suitor was just too sad.

But love, and diamond ring resales, can go wrong in other ways.

Take Josh Opperman. He had a broken engagement. He tried to sell his ring back, and, he says, “the place I brought it from would only give me store credit.” (Rarely valuable for a man out of love.) So he took it around to a few other places, and, says Josh, “the highest I was offered was 35 percent of what I paid for it.”

So Josh turned his heartbreak into a business. He started a website called I Do…Now I Don’t. It’s a place to resell second-hand engagement rings and jewelry. He says he was able to sell his $10,000 ring for about $7,000.

Jewelry appraiser Neil Beaty says when it comes to the resale value of diamond rings, people need to keep their expectations in check.

“Diamonds as an investment almost always fail,” Neil says. The cost — and appraisal value — of a piece of jewelry isn’t just the value of the diamond plus the value of the gold or platinum. You’re also paying for the cost of making the piece, and selling it to you, the rent, the middlemen, the intimidatingly clean jewelry cases. Just like a new car or a couch, the resale value often falls once you get your hands on it. “People don’t think of diamonds as a consumer purchase,” Neil says. “They are.”

Now depending on the diamond, there are some exceptions to this. Diamond values fluctuate based on supply and demand (And no, the diamond heist was too small in the scheme of things to change those prices).

But, Neil says there is still value in these purchases. When your wife looks at her ring and is reminded that she is loved, that matters.

The investment is just in the relationship, not the stone.