Differentiating between broken rocks and arrowheads is relatively easy. Arrowheads have a point, an edge, and a base. They needed to be made from strong stone that could be sharpened and light enough to fly true. Quartz, limestone, and marble all had their uses, but arrowheads were mostly made from chert, obsidian, and flint. Regionality plays an important part in the stone used for arrowheads. Chert, for instance, was commonly used by Native Americans in Missouri and Illinois. When you find an arrowhead, cross-reference the material to see if it was something locally available.