In general flint is believed to consist of microcrystalline alpha-quartz. Closer investigation reveals a very complex structure of pseudohexagonal plates forming grains. These plates consist of even smaller particles held together by monolayers of water. The question arises, where in this structure the impurities, in total up to 3%, are situated. Iron for instance cannot be removed by different concentrated acids. So it cannot be outside the plates. On the other hand iron is leached out by soft solvents such as solutions of ammonia and salt. So the impurities must be located between the monolayers. Measurements of the grain size of different sorts of flint were carried out by x-ray diffraction. Investigations like this play a part in the understanding of weathering of flint artifacts and their colors. -- AATA