Defining minerals and rocks by examining them under a polarizing microscope. A simple, fast and cheap tool for analyzing the composition and provenance of pottery, stone, plaster, etc. When you polish rock-forming mineral crystals, they become permeable to light. Even when it comes to a tool that has been processed by my humans (pottery), the original crystals remained or new crystals were formed. Not relevant for metal (no penetration of light) or glass (no crystalline structure). Gives information on the composition, origin, production process and post-cooling processes.