I think the way coal is set up could be easily improved (think positive, here)

Currently, coal is almost as difficult to dig as platinum, with iron being the easy one - it ought to be
really easy to dig coal, a no-brainer really

It's the perfect mining training material, being easy to dig out, simple to use - just take a coal lump to the customer for burning.
When it comes to "getting rid" of the coal lumps you just dug out, NPCs who purchase raw materials accept coal too, but pay
zero tria per lump. This is too little! They should pay at least 1 tria per lump, otherwise why bother digging it out? A few tria for the bother of getting the coal, not to mention the labor of hauling it to town...

Coal is right now used mostly by the players as an ingredient in making steel, where we're talking another kind economy altogether...
But the possibility to sell to NPCs should be maintained, IMHO, if only as an outlet to prevent littering

So my simple and easy-to-use suggestion is as follows: Set coal price to 1 tria, and make it twice as easy as iron to dig out.