Mankind has known how useful minerals and rocks have been for a very long time indeed. In fact, all the earliest tools that we know about are all minerals, since organic materials have rotted away, and manmade materials are very recent. The earliest tools discovered are of stone, of flint or obsidian . The earliest pictures are cave paintings made with hematite . Gradually mankind learned to make tools with metal, first with copper and bronze , then iron and steel .
Steel is mainly iron, but has other metals in as well.
Well, all these tools have a sharp edge. Wood has always been used, and stone and bronze are still used today. The tools that named the age were the tools with an edge. Flint and obsidian have the important property that when you hit them, they splintered into sharp flakes. You didn't need to sharpen them since they were already sharp.