.....and in very controlled conditions, and technically the stone is still not "on fire" , its simply being heated to the point of melting the stone. as for the MONOLITH in the middle of vatican square, never ever going to CATCH FIRE unless you topple it, move it into a kiln, and subject it to high heat for a long time and in THAT environment you'll see the miniscule amounts of "fire" it produces as the heat burns off any combustible substance possibly trapped in the stone from its creation millions of years ago from a similar but natural process.