Can someone advise me if a diamond is a good long term investment?? At this time it can be very risky to invest in the stock market. We have had good luck with art, but I really want to buy a large quality stone (3.5 - 5ct.) But I just don''t know if it would be a safe investment. I''m expecting to spend alot of money.. and if I wanted to sell in 10 years, what could I expect?