Black dendritic films of various visually indistinguishable black manganese oxides, may consist of birnessite, coronadite, cryptomelane, hollandite, ...
You definitely have some interesting ground to scan and congratulations on the discovery of some nice examples of petrified wood. Out back of where I live are some long abandoned coal mine tailings and I will find pieces of petrified wood scattered about the old miners dug up from below. Nothing of real gem quality, but fun to walk the dogs around and pick up interesting things and in it's own way tell a story of events and a time long, long ago.