OK, here we go again...

Pure flint does not spark at all.
With a flint and steel, it is ONLY the steel that burns.
All of the firesteels have NO flint in them...
With a firesteel, it is ONLY the fero rod that burns.
It is made out of Mish-metal, which is a combination of several of the rare earth elements(which are rather interchangeable as they are all so close in molecular structure that they all behave almost identically).
Some do add magnesium to help.
They can be 'sparked' by ANY sharp, hard object. Broken glass works great, as does any of those carbide knife sharpeners. A REAL flint works great to 'spark' them with too!
What you may have heard about needing carbon steel to strike a flint with, does NOT apply to a firesteel, as it takes the place of the STEEL in a flint and steel set, not the flint. And the steel striker takes the place of the flint!
Mish-metal, aka firesteel, aka ferrocerium is a VERY soft metal and so can be cut by steel(and MANY other things). Steel is softer than flint and so can be cut by flint.
Mish-metal is VERY much softer than flint and and therefore be cut VERY easily by flint.

I know I get a little too perturbed about this, but knowing how these things work, makes them a LOT easer to use when thing are not going right, and you have to improvise.