Prospecting now only shows there is ore or gem, it does not show type of ore OR deposit size, which is missed dearly from the old mining system. It made mining interesting, and not quite such a chore.
I would be satisfied with simply being able to see specific types of ore through symbols, and using prospecting to see the size of the deposit.
The only predictable and consistent symbols we currently have are bone, void stone, unstable faultline, and red stone. At the very least we need symbols that signify where ore/gems are, and new symbols that signify a room containing both ore AND gem deposits. Preferrably symbols that change as the resources are mined out, as with the old system, although that is less important since mining is now a continuous task.
Small edit: I forgot about coal, but you probably wouldn't.
![Razz :P](./images/smilies/icon_razz.gif)
Coal needs a symbol too!
Second edit: Show us stone in mine prospecting. It's confusing that the layers condense and you can't tell where things are and how close something might be when you're trying to dig to it.