When evaluating Potassium Feldspar (K-feldspar), the primary focus should be on chemical purity and mineralogical composition. K2O (Potassium Oxide) content should ideally be above 10% for high-grade applications. You must also monitor the Fe2O3 (Iron Oxide) levels, which should be less than 0.1% for high-end ceramics and glass to prevent discoloration. Additionally, verify the Al2O3 (Alumina) content, typically ranging between 17% and 19%, as it enhances the mechanical strength and chemical durability of the final product.