Only the coal resource does this: when dumped over a perfectly flat ground (stone/slag/garbage base covered by dirt), and then scooped over, sometimes coal comes with bits of dirt, and the top ground layer contains small spots of coal, after that.
That issue was first spotted years ago. Happens only with coal. Any other kind of resource piles are scooped without any contamination. Only coal is bugged.
That is how I store resources, as a piles, and all other kinds except for coal, can be mined directly into storages, but for coal, a dedicated sorting plant is needed.
