Investments backed by physical Diamonds?

My gut says such an ETF would be impossible to create. The metals are elements that are definable so there's no question what we are trading. Most bars are stamped '.999 fine' and while we can go off on a tangent of coins, collectables, etc, let's not. I give you a bag of little gold bars, a few hours later, it's assayed, recast into an ingot of larger size and ready to deliver against a contract.

Let's assume Beltrame's concerns are unfounded. Diamonds are not homogeneous as gold (or other metals) are. The same pound of the stuff can range from industrial grade used for expensive sand paper, to a small number of large gems that are priceless. This precludes a physical asset ETF, in my opinion.

Now, you might suggest that houses fall into a similar category. Schiller created an index for house prices, and one might be able to do the same for diamonds if it doesn't already exist. Defining it is beyond me, but I can see an index for the value of a particularly defined diamond criteria using the available sales data.

Edit - For what it's worth, it seems attempt at this is in the woks - Diamond ETFs in the Works — Will Investors Bite?