Telescope for measurement of optic angle of mica.

Ruthberg, Stanley

doi:10.6028/jres.065c.015

Cited by 2 publications

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“…The apparent optic angle, that is the emergent optic axial angle as viewed in air, is a property of the crystal sensitively dependent upon the magnitude of the three principal refractive indices and is an easily measured quantity. The equipment used by us is described elsewhere [31]. A precision of better than ±5′ arc is achieved for good specimens.…”

Section: Experimental Methodsmentioning

confidence: 99%

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

Ruthberg¹,

Barnes²,

Noyce³

1963

J. RES. NATL. BUR. STAN. SECT. A.

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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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Section: Experimental Methodsmentioning

confidence: 99%

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

Ruthberg¹,

Barnes²,

Noyce³

1963

J. RES. NATL. BUR. STAN. SECT. A.

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“…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) .…”

Section: Methodsmentioning

confidence: 99%

Thermal behavior of muscovite sheet mica

Ruthberg¹

1963

J. RES. NATL. BUR. STAN. SECT. A.

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The three sp ect ral types of muscovite shee t mica, i.e. , very pink ruby, ligh t gree n, a nd dark green, w ere subj ected to heat tr ea tm ents a t tempera t ures up to 600°C. The c ha nges in the apparen t optic a xial a ngle and in the absorp tion spectra (0.3 to 15 JJ. ) were st udied along with color.The d iff erentiation of muscovi te sheet ac cording t o these spectral typ es extends to t he beha vior of apparen t op tic axial a ngle and to certain regions of t he spectrum under hea t treatmen t. The pink associated a bsorp tion region (0.47 t o 0.6 JJ. ) can be enhan ced or blea ched away by appropriate t hermal trea t men t, althoug h t he assoc ia ted infrared multiplet at 3 to 3.5 JJ. is lit tle a ffected . The abso rp tion ba nd at 12 JJ. increases in intensity wi t h te mperat ure o f t reatm en t. It is s uspected t hat t he 0.47 to 0.6 JJ. a bsorp t ion is t he r esult of color cen tel's.It has been shown th at m easurable differ ences exist in appar en t op tic a xial angle and absorp tion sp ectrum , as well as in color, for muscovi te sheet micas. 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). 1The 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 . Experimental ProceduresThe 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. Color was determined by compa rison with the previously selec ted standard samples. SpecimensThl'Oe categories of mu covite sheet wer e chosen . 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.Crystal sh eets wer e all of high qu ali ty, V-I to V-4 [3), with origins in India, Brazil, T angan yika, and th e Uni ted States.As appropriate combin a tion of visual color determ in ation and r estriction to magni Lud e of apparen t optic axial angle can as ure selection of th ese endtyp es, su ch procedure was used for sample choice. Specimens were fir t selected according to visual color. They wer e t hen picked for m agni tude of appal'cn t op L ic axial angle. The very pink ruby specimel1:6 were 1'c trictecl Lo an0 1es between 68° and 72. 5°. Ligh t gr eens wer e restricted t...

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Telescope for measurement of optic angle of mica.

Cited by 2 publications

References 0 publications

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

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

Thermal behavior of muscovite sheet mica

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