Flint powder is a 325 mesh ground silica that is predominantly used in glazes. Flint flour is a 200 mesh ground silica most commonly used in clay bodies. Flint is universally used in bodies and glazes and modern machinery can grind it to any size needed. It is very likey that you have never actually seen real flint and will not be able to find the true material from any supplier. The terms flint, quartz and silica have come to be used interchangeably in ceramics and you will see them all employed in recipes; they are all the same thing. However, most correctly, the material used in ceramics is called simply "silica". "Quartz" refers to the macro-crystalline mineral we find in nature. The terms "pottery quartz" or "potter's sand" likewise refer to silica. The term "flint" surfaces most often when referring specifically to the tools ancient peoples made from the micro-crystalline mineral.