Interesting idea but diamonds are more and more considered to be bloody and a "fake" industry, in the sense that one single company buys all the world's supply and they dictate the price. As others have said before, it's far from what blockchain technology stands for.
Actually, the opposite is the truth. It used to be a monopoly by DeBeers. In the past few decades, more and more companies have entered the market and created competition and in the past 15 years, with the rise of online platforms for diamond traders where they can buy and sell their diamonds online via a trusted third party it has become more and more democratized.
Incredibly enough, most people thought that the control of DeBeers was the reason the price of diamonds were moving up however the less control there is over the industry, the more the price rises! When looking at charts you can see the correlation.
The above two things are the reasons that diamonds have become more popular (maybe not with you personally but with most of the world) and the reason a number of companies have integrated them into the blockchain technology. Up until now, all diamonds were always traded with a handshake agreement, whereas now the diamonds can be traced back each step of the way all the way to the source. It's still in its infancy but that's the beauty of everything - there's always the ground floor you can get on.
Diamonds which until now weren't a part of the financial industry either, are also being added there. Most prominently by the company Live Rates Feeds (the parent company of KELA) but also by a few other industry players.
I hope this clarifies any misconceptions about the diamond industry, its relation to blockchain and its potential.