Summary: Diamonds have done relatively well as an investment class over the past few years but selling the precious stones is tricky as their value varies from person to person. De Beers and other diamond marketing businesses are known to restrict the supply of diamonds, while diamond valuations can be disputed. On the positive side, there will inevitably be a decline in the supply of freshly mined material.
Key take-out: If you believe the value a reputable dealer puts on a diamond, ask what it would be worth on re-sale. Chances are an investor would need to keep the diamond for a long time to cover that gap.