A d etailerl experimental study of color, apparent optic angle, anci absorption spectrum (0.3 to 16,u of A) indicates that there arc basic chemical and structural differences in muscovite micas. Color identification is bascd upon s pectrophotometer measurements. A m ethod for quantitative evaluation of absorption band activity is defined so t hat single and mUltiple band intensities within the sp ectrum of an individual specimen and within spectra of different specimens can be compared. Three basic spectral t ypes exist for the 0.3 to l,u A region which are comprised of various weak lin es and absorption regions lying alon g the base of a deep absorption edge ncar 0.32,u . Of the three spectral types, on e is a ssociated with ruby micas, whilc the other two are associated with dark green anrl light green micas. The activities of numerous lin es and bands arc reported. It is s hown t ha t apparent optic axial angle is related to t he position of t he d eep band edge except for a certain class of ruby sp ecim ens which show anomaloLl s val ues . A d efinitive characteri zation of muscovite s heet is formul ated in t erms of the absorption coefficients at 0.'14, 0.49, and 0.58,u. Direct assoc ia tions arc s hown between certa in lines in thc vis ible A range and certain bands in the n ear infrared , while the activities of a number of bands in thc middle infrared arc correla ted to color.

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