1.1 This classification covers the determination of commer-cially available natural muscovite block mica and is intended to be independent of the basic color of the mica or its source.
1.2 Muscovite mica is characterized by having an optical axial angle between 50 and 75° (see Appendix X1); and has a weight loss when heated for 5 min at 600°C not exceeding 0.2 % (based on the weight after drying at 120°C).
