Issues and controversy: the measurement of crystalline silica; review papers on analytical methods

This article reviews the analytical methods for crystalline silica polymorphs and summarizes promising techniques for compliance with health-related regulations. X-ray diffraction analysis appears to be the most promising method of determining quartz and cristobalite content at this threshold in many bulk mineral and chemical systems. Other analytical techniques can be used in some mineral and chemical assemblages, but usually lack polymorph specificity or sensitivity. All analytical methods benefit from concentration techniques that do not alter crystalline properties of silicas. National Institute of Occupational Safety and Health (NIOSH) Analytical Method 7601 as written suffers from destruction of the mineral residue containing crystalline silica polymorphs after dissolution of many silicate minerals in phosphoric acid and may also include digestion-resistant silicate minerals, but it is a promising concentration method for other analytical methods such as NIOSH Analytical Method 7500 (X-ray diffraction).