From my experience (such as it is), I can say that after you get the "core" right the rest isn't too hard, but I still have a hell of a time getting the core the right shape to start with! :cursing:
I located some very fine grained rhyolite that formed in hexagonal columns. (Not all rhyolite is either fine grained or forms in columns.) It looks a good bit like black flint with a few little white specks in it, and it has conchoidal fracture like flint, but this particular supply has the advantage that the columns tend to break off more or less flat on top, which really helps get the thin blades needed to make some "flints". Rhyolite (igneous rock) was used by some Native Americans in locations where flint and chert (sedimentary rocks, more or less) were rare, it really acts very much like flint. Makes good gunflints, (after I went through maybe 30 pounds of it to get the hang of making the gunflints. :redface: )
Also works really well for flint and steel, but a lot of stuff will do that.