Feldspar quality is primarily determined by its chemical composition, specifically the levels of Alumina (Al2O3), Potash (K2O), and Soda (Na2O). For the glass and ceramics industries, the Iron Oxide (Fe2O3) content must be below 0.1% to prevent discoloration. Buyers should request a Chemical Analysis Report (XRF) to verify the mineral purity and ensure the particle size distribution (mesh size) aligns with their specific manufacturing requirements, such as 200 mesh for ceramics or granular form for glassmaking.