Correlation of muscovite sheet mica on the basis of color, apparent optic angle, and absorption spectrum

Abstract

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.

Thermal behavior of muscovite sheet mica

“…The details of m easurem ent of appar en t optic axial angle, absorption sp ectrum, and color ar e as b efor e [1,2) .…”

“…Comparisons of sp ectral variations are again made in terms of the r esonance absorption coefficient (below b ackground), cx x(R ), defin ed with r espec t to an a,ppropriately pl aced base lin e as (1) wher e Til. is the transmission at t he r esonance band center , Tb is the value at the base line for t he same wavelength, and t is t he s pecimen thickn ess.…”

“…These wer e very pink ruby, light gr een , and dark 1 Figures in brackets indicate tb e literat ure references a t tho end of tb is paper. gr een , which represe n t the three end-typ es as d efin ed in th e earlier work.…”

“…These diff er ences indica te that there must b e basic ch emical and structural variations. They fur th er provide a quan ti tative, t hou gh complex, categoriza tion of the material [1). 1 The present p ap er r eports the effect of h eat tr eatm en t on color, apparent optic axial angle, and absorp tion sp ec trum for sever al of th e r eprcsen Lative categories of the m aterial so e tablish ed .…”

“…They fur th er provide a quan ti tative, t hou gh complex, categoriza tion of the material [1). 1 The present p ap er r eports the effect of h eat tr eatm en t on color, apparent optic axial angle, and absorp tion sp ec trum for sever al of th e r eprcsen Lative categories of the m aterial so e tablish ed . The tr eatm en ts wer e a t temper atures of 600°C and less, usually consider ed to b e below th e decomposition poin t .…”