A shelf of Cracked Cap Polypore(Phellinus robiniae), from a dead Black Locust tree collected in Va.  This type of fungus has been used traditionally as an aid to friction fire methods, particularly to aid the ember gaining heat in the tinder bundle to be ignited to full flame.  When an ember is created with friction methods or spark methods(flint and steel), fungi can help grow the ember grow, or it can catch the spark itself when specially prepared.  The solid raw shelf fungus itself can even be used as a hearth for friction drilling, and it has worked here with pithy drills such as elderberry and mullein.  See pics for measurements.  The shelf here should be enough for dozens of tinder bundles if shredded in fine shaving and added to tinder bundle or in hearthboard notches.