This is a small mod AaronG85 modified based on the work of Claymore.
This changes the boulders (ResourceStones) in game to give you a small chance at mining: Coal, Potassium Nitrate Powder, Lead, Sand and Clay
This also gives you a rare chance of mining: Brass, Silver, Gold and Dimond
Also gives the ability to mine a small amount of iron from terrestrial stone boulders.
The percentages can be changed higher or lower to suit your gaming needs via the blocks.xml.
NOTE: This changes all boulders currently, If anyone has any tips on how to make the changes ONLY affect the ResourceStone Boulder, not the specialized boulders, they are very welcome to PM him so he can implement it.
The forum topic of the mod is here.