Making fire using only rocks to generate a spark has been on my bucket list for a number of years. Recently I watched a video demonstrating this from David Canterbury that inspired me to try again. Like many fire methods it can mainly depend on the proper materials in order to accomplish it.
In past efforts I had acquired an iron pyrite nugget that was the right size (large enough to hold by hand) and texture where the non-crystal area is the best area to strike in order to create sparks. Historically horse hoof fungus that contains a layer known as amadou has been used for tinder but I had rummaged through some of my firecraft materials and came across some excellent inonotus obliques fungus or chaga as my tinder. The soft punky areas of chaga works the best for catching sparks.
I used my knife to rub an edge of the chaga in order to make powder which created more surface area for catching the weak sparks that iron pyrite produces. Unlike ferrocerium rods where a single strike produces a shower of hot sparks, the rapid succession of striking the pyrite using the flint produces the best results for the weaker sparks to succeed.
Once a spark is caught in the tinder you can bolster it with the surrounding material followed by a gentle breath to help it grow. Once the coal is established it can be transferred into a bird’s nest of tinder (in my case jute fiber) and coaxed into a flame.