Quality grades and specifications explained

Industrial minerals are not commodities — they are specification products. The same mineral can range from a low-value agricultural grade to a high-value pharmaceutical grade depending on processing and purity.

Particle size is the most critical specification for most applications. It is expressed in microns (µm) and characterised by D50 (median diameter), D97 (97% of particles below this size), and sometimes D90. Mesh size is an older unit still used in India: 300 mesh = approximately 45 µm, 400 mesh = approximately 37 µm, 500 mesh = approximately 25 µm. For ultra-fine applications like coatings, particles below 5 µm (D97) are standard.

Whiteness and brightness are critical for applications in paper, paints, and plastics. Brightness is measured using the ISO 2469 standard (R457 brightness). A brightness of 92–95% is standard for coating-grade calcium carbonate. Talc brightness varies from 85% for industrial grade to over 95% for cosmetic grade.

Moisture content is critical for minerals used in plastics compounding and powder coatings. Excess moisture causes processing problems (splay, voids) and degrades the final product. Specification limits vary by application but are typically 0.2–0.5% maximum.

Chemical purity — especially calcium carbonate (CaCO3) content for calcite, MgO content for dolomite, SiO2 content for feldspar — is specified precisely for different end uses. Heavy metal limits (lead, arsenic, mercury, cadmium) are mandatory for food, pharma, and cosmetic applications.