I think you have already heard from one of the world’s greatest experts and authors on gem valuation, but I’ll add a couple of things. I think the guide here (and note the word “guide”) gives retail prices. Unless you are setting stones and have a recognized website or bricks and mortar store, you are unlikely to get retail prices for loose gemstones. So right away there is the chance that you bought at retail and are selling at wholesale, a sure way to lose. Then there is the question of the quality of what you bought. The guide gives a range of prices and these depend on clarity and color and cut for any given weight. Unless you are an expert, fine distinctions of color and clarity and cut may be beyond you, yet they may mean a lot of dollars when it comes to valuation.
When someone who has spent his life in the gem trade (and written the book_Secrets of the Gem Trade_,
which I have at my desk right now) tells you this is a full time job requiring lots of experience, you should listen well. Does it not make sense that if it were as easy as looking up in a guide here and then forking over money, then everyone would be doing it? I do little buying and selling, mostly to cut myself, but I have been a lapidary since 1983 and a faceter since 1995 and taken the GIA training as a gemologist. Even at that, there are lots of things I would pass on because I just don’t know the particular market. Sorry you have not succeeded, but you can enjoy purchasing for the joy of ownership or buckle down and do the hard work of learning how to profit in the gem world. You also might consider going on a trip with recognized experts to a gem exporting country where these experts could guide your purchases and teach you what you need to know. My friend Dan Lynch is going to give a presentation on buying gems in East Africa at this year’s Faceter’s Frolic in Franklin, NC and I know that Roger Dery sometimes takes others with him on buying trips to Arusha and elsewhere in Africa. If you come to the Franklin Frolic, stop by my table and I can sell you some rough at decent prices and then you can make contact with cutters to cut it for you. You would end up with nice stones and might even be able to make a little money. You could, for example, buy some pink tourmaline at $80/gm, get 30% yield on a 2.5 gm stone and sell your 3.75 ct stone for $100-$150/ct. If you bought at $200 and sold at $375, you’d split $175 with the cutter, and that would be a slim profit. If you chose wisely and could get $150/ct, you’d have $362.50 in profit and could pay the cutter $125 and still take home some decent money. I’m giving a talk at the Frolic on maximizing yield, only one of the things you need to know if you’re buying rough. Help, I’m talking about gems and can’t shut up! Hope this helps.