Well, it could be because these are metal ores and not gems...the "spot" price of metals is listed on the various stock exchanges every day and it changes, so any valuation on here would be out of date rather quickly. If you can determine the specific gravity of the ore and the specific gravity of the host rock, then you can determine by simple math how far along the continuum from host rock to pure metal your sample is. This will give you an approximate percentage of purity, assuming there is mainly one metal in the ore. Then you can find a refiner who will take ores and see what percentage of "spot" price they will pay you. So it is spot price X percent purity X percent of spot price paid by refiner. If the ore has both silver and platinum, you will just have to send the ore for an assay to the refiner and they can determine the percentage of the various metals. They keep careful account of these things and pay you for the ore's yield. You are asking the impossible if you want a gem valuation table to evaluate your ore. If your ore is decent stuff with a good percentage of metal in it, the refiner wants your business and will be only too happy to work with you and provide evidence of their assay. If you don't feel you can trust a refiner, there are firms which will do the assay for you and certify it, for a price. Many times a country will have done studies of the ores available in mining regions and their reports will give an idea of the purity that has been found in a particular area, so contacting the national mining dept. may help with some info. In the end, however, you will have to have an assay, as there is no way to tell whether you have happened on something better or worse than has been discovered and examined before.