Spectroscopic Characterization of Minerals and Their Surfaces

Chapter 10 Three-Dimensional

Thermoluminescence

Spectroscopy

of

1

Minerals 1

2

John R. Prescott , Riaz A. Akber , and R. K. Gartia

1Department of Physics and Mathematical Physics, University of Adelaide, Adelaide 5001, Australia Physics Department, Manipur University, Imphal 795003, India

Downloaded by PURDUE UNIV on April 6, 2016 | http://pubs.acs.org Publication Date: November 29, 1990 | doi: 10.1021/bk-1990-0415.ch010

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A new application of thermoluminescence (TL) to the study of minerals i s described. The intensity of TL light emission as a function of both temperature and wavelength defines a three- dimensional picture which is characteristic of a particular mineral or group of minerals. The apparatus i s briefly described together with i t s application to the study of the physical structure of some a l k a l i feldspars. Examples are given of a K-rich and Na-rich feldspar and a potential method is discussed for identifying the nature of the phases of samples of mixed K/Na composition. The work described here had i t s genesis i n a project to study thermoluminescence (TL) i n a range of feldspars, with the aim of systematising their general characteristics as an aid to TL dating. Some of the results of this study are presented here. For the present work, discussion i s confined to the consideration of the information that TL can give about some aspects of physical structure, including microstructure, i n the a l k a l i feldspars. Consideration of trapping and luminescence centres w i l l be only incidental to the discussion; and the broader study w i l l be described elsewhere. The second purpose of the work i s to describe the use of three-dimensional (3-D) spectroscopy i n which the TL intensity i s measured as a function of both temperature and wavelength. Feldspars The feldspar minerals are aluminosilicates of a l k a l i and a l k a l i earth cations and are chemically classified by the mole percentages of three end-members: orthoclase (Or: KAlSi 0 ) albite (Ab: NaAlSi 0 ) anorthite (An: C a A l S i 0 ) . The three constitute a ternary system with extensive solid solutions along the Or-Ab and Ab-An axes. The nomenclature on the basis of the mole percentages 3

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0097-6156/90/0415-0180$06.00/0 © 1990 American Chemical Society

Coyne et al.; Spectroscopic Characterization of Minerals and Their Surfaces ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

10. PRESCOTT ET AL.

Three-Dimensional Spectroscopy

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o f t h e end-members i s shown i n F i g u r e 1 w h i c h a l s o shows t h e approximate l o c a t i o n o f t h e r e g i o n o f phase s t a b i l i t y . The TL e m i s s i o n s p e c t r a o f f e l d s p a r s have been r e p o r t e d i n t h e p a s t by a number o f workers ( 1 - 6 ) . R e c e n t l y , measurements o f TL emission s p e c t r a o f f e l d s p a r s w i t h the help o f spectrometers o f much i n c r e a s e d s e n s i t i v i t y have been r e p o r t e d ( 7 - 9 ) . TL s p e c t r a p r e s e n t e d i n t h i s paper a r e r e c o r d e d w i t h t h e h e l p o f a new h i g h s e n s i t i v i t y s p e c t r o m e t e r b a s e d on F o u r i e r t r a n s f o r m s p e c t r o s c o p y .


The 3-D S p e c t r o m e t e r A p p a r a t u s f o r t h e s t u d y o f TL i s u s u a l l y s i m p l e i n i t s d e s i g n and p r i n c i p l e s ( s e e , e.g., ( 1 0 ) ) . The sample, p r e p a r e d e i t h e r as g r a i n s o r a s l i c e a f r a c t i o n o f a mm t h i c k , i s p l a c e d on an e l e c t r i c a l l y h e a t e d p l a t e i n an i n e r t gas and, as t h e temperature i s r a i s e d , the l i g h t output i s recorded u s i n g a p h o t o m u l t i p l i e r . The graph o f TL i n t e n s i t y vs temperature so o b t a i n e d i s known as a "glow-curve". I n t h e p r e s e n t c o n t e x t i t i s b e t t e r d e s c r i b e d as a "2-D g l o w - c u r v e " , t h e dimensions b e i n g i n t e n s i t y and t e m p e r a t u r e . U n d e r s t a n d i n g o f t h e b a s i c TL phenomena i s g r e a t l y a i d e d by t h e i n f o r m a t i o n o f "3-D g l o w - c u r v e s " i . e . , TL e m i s s i o n s p e c t r a i n w h i c h t h e i n t e n s i t y i s d i s p l a y e d as a f u n c t i o n o f b o t h t e m p e r a t u r e and w a v e l e n g t h . I n t h i s mode, temperature peaks a r e c h a r a c t e r i s t i c o f t r a p s and t h e w a v e l e n g t h peaks c a r r y i n f o r m a t i o n about t h e charge r e c o m b i n a t i o n s i t e s (luminescence c e n t r e s ) . The advantages o f 3-D s p e c t r o s c o p y were r e v i e w e d by Levy (11) and f u r t h e r by J e n s e n and P r e s c o t t ( 1 2 ) . The d e s i g n e r o f a 3-D s p e c t r o m e t e r has t o a d d r e s s two c h a l l e n g i n g problems: t h e low i n t e n s i t y l e v e l , and i t s v a r i a t i o n w i t h temperature and hence w i t h time. I t i s c h a r a c t e r i s t i c o f TL measurements t h a t t h e temperature changes m o n o t o n i c a l l y d u r i n g observations. C o n s e q u e n t l y s p e c t r a l measurements must be made c o n t i n u o u s l y o r , i n p r a c t i c e , as d i s c r e t e samples o v e r s p e c i f i e d temperature i n t e r v a l s . The p r e s e n t equipment, based on F o u r i e r - t r a n s f o r m s p e c t r o s c o p y , makes use p r i m a r i l y o f t h e s o - c a l l e d "throughput advantage", i . e . , t h e d a t a c o r r e s p o n d i n g t o a l l w a v e l e n g t h s o f l i g h t a r e c o l l e c t e d s i m u l t a n e o u s l y from an extended s o u r c e . These c h a r a c t e r i s t i c s i n c r e a s e t h e s e n s i t i v i t y f o r TL e m i s s i o n s p e c t r o s c o p y and have a c h i e v e d t h e aim o f making i t p o s s i b l e t o s t u d y TL e m i s s i o n phenomena a t low r a d i a t i o n l e v e l s , comparable w i t h those r e c e i v e d by t h e m i n e r a l o r phosphor samples d u r i n g t h e i r actual application. The equipment and i t s d e s i g n c r i t e r i a have been d e s c r i b e d i n d e t a i l e l s e w h e r e ( 1 3 ) . Only i t s e s s e n t i a l f e a t u r e s w i l l be d e s c r i b e d here. I n i t s b a s i c d e s i g n , t h e equipment i s s i m i l a r t o a 2-D TL g l o w - c u r v e system as d e s c r i b e d p r e v i o u s l y , b u t w i t h t h e a d d i t i o n o f a m o d i f i e d Twyman-Green, M i c h e l s o n t y p e , i n t e r f e r o m e t e r between t h e oven and t h e p h o t o m u l t i p l i e r . As t h e sample i s h e a t e d , t h e TL s i g n a l i s r e c o r d e d w h i l e t h e movable m i r r o r o f t h e i n t e r f e r o m e t e r i s s c a n n i n g a g i v e n o p t i c a l p a t h d i f f e r e n c e i n a p r e s e t number o f s t e p s . The i n t e r f e r e n c e p a t t e r n c o r r e s p o n d i n g t o each one-way s c a n



SPECTROSCOPIC CHARACTERIZATION OF MINERALS AND THEIR SURFACES



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i s c a l l e d an i n t e r f e r o g r a m . Each i n t e r f e r o g r a m i s t h e F o u r i e r t r a n s f o r m o f t h e i n p u t spectrum d u r i n g t h e c o r r e s p o n d i n g t e m p e r a t u r e i n t e r v a l and I t s i n v e r s e F o u r i e r t r a n s f o r m s u b s e q u e n t l y y i e l d s t h e spectrum. F o u r i e r transform spectroscopy i s mainly a p p l i e d t o the lower wavenumber o r i n f r a r e d r e g i o n . S p e c i a l c o n s i d e r a t i o n s were r e q u i r e d t o a p p l y t h e t e c h n i q u e i n t h e v i s i b l e / U V r e g i o n . The r e s o l u t i o n o f t h e equipment i s n o r m a l l y about 20 nm around 500 nm b u t t h i s o f f e r s no s e r i o u s problem, because i n most c a s e s t h e TL e m i s s i o n i s e x p e c t e d t o be b r o a d band w i t h f u l l w i d t h a t h a l f maximum e x t e n d i n g up t o a few t e n s o f nanometres. The t o t a l i n t e n s i t y o f t h e TL l i g h t spectrum from t h e samples v a r i e s c o n t i n u o u s l y w i t h t e m p e r a t u r e , and hence w i t h t h e m i r r o r d i s p l a c e m e n t , o v e r t h e s a m p l i n g time i n t e r v a l . The i n t e r f e r o g r a m i s superimposed on t h i s n o n - c o n s t a n t l e v e l . As t h e F o u r i e r theorem i s s t r i c t l y only v a l i d f o r constant s p e c t r a l emission, misleading i n f o r m a t i o n ( f a l s e d e t a i l ) i s produced by t h e raw i n t e r f e r o g r a m s . The i n t e r f e r o g r a m s a r e c o r r e c t e d f o r t h i s e f f e c t . The s p e c t r a a r e f u r t h e r c o r r e c t e d f o r t h e s p e c t r a l response o f t h e equipment i n t h e 350-600 nm range. The c a l i b r a t i o n i s h i g h l y s t a b l e from day t o day b u t i s r o u t i n e l y c a l i b r a t e d under t h e c u r r e n t o p e r a t i n g c o n d i t i o n s by i n t e r f e r o g r a m s w i t h t h e 633 nm l i g h t from a He-Ne l a s e r . The system has now been upgraded t o e x t e n d t h e response t o c o v e r 250740 nm. The r e s u l t s may be d i s p l a y e d e i t h e r as an i s o m e t r i c 3-D p l o t of i n t e n s i t y vs temperature and w a v e l e n g t h o r as a c o n t o u r map. I n d i v i d u a l i n t e r f e r o g r a m s c a n a l s o be summed t o d i s p l a y a c o n v e n t i o n a l 2-D glow-curve o v e r t h e f u l l temperature range. Results S i x t e e n samples on t h e Na-K a x i s ( F i g u r e 1) have been s t u d i e d . I n what f o l l o w s , o n l y t h e " n a t u r a l " TL (NTL) i s c o n s i d e r e d i . e . , t h e TL i n t h e sample "as r e c e i v e d " w i t h o u t any p r i o r h e a t i n g o r additional radiation. H i g h P o t a s s i c F e l d s p a r s . A h i g h p o t a s s i c f e l d s p a r from K i n g s t o n , South A u s t r a l i a , (mole % K:Na:Ca - 81:18:1) r e p r e s e n t s a t y p i c a l NTL spectrum f o r members o f t h i s group. F i g u r e s 2a and 3a show t h e 3-D and c o n t o u r p l o t s r e s p e c t i v e l y . An e m i s s i o n band n e a r 400 nm w i t h FWHM o f about 40 nm i s prominent i n t h e g l o w - c u r v e . The NTL peaks o c c u r between 250-350°C f o l l o w e d by a n o t h e r h i g h temperature peak around 500°C. The S o d i c End Members. F i g u r e s 2b and 3b show t h e NTL b e h a v i o u r o f an a l b i t e from A m e l i a , V i r g i n i a , U.S.A. w h i c h has v e r y low Κ and Ca c o n t e n t (K:Na:Ca: - 2:98:-). The main e m i s s i o n band i s around 560 nm w h i c h peaks n e a r 320 C. T h i s b r o a d ( i n w a v e l e n g t h and t e m p e r a t u r e ) peak i s c h a r a c t e r i s t i c o f l o w K, low Ca f e l d s p a r s . There i s a l s o a low i n t e n s i t y e m i s s i o n a t s h o r t e r w a v e l e n g t h s and h i g h e r t e m p e r a t u r e s . The A m e l i a a l b i t e e m i t s two t o t h r e e t i m e s more TL l i g h t p e r mg t h a n t h e h i g h p o t a s s i c end-member f e l d s p a r s and c o n s i d e r a b l y more t h a n t h o s e o f i n t e r m e d i a t e c o m p o s i t i o n . e




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Figure 2. Continued. 3-D spectra of alkali feldspars. For each sample, the triangle indicates the mole composition on the ternary diagram. (c) Mount Soma "sanidine" (d) Wisconsin moonstone




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Figure 3. These contour diagrams are for the same samples and occupy the same relative positions as the compounds in Figure 2. (Reprinted with permissionfromref. 13. Copyright 1988 Optical Society of America.)


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I n t e r m e d i a t e A l k a l i F e l d s p a r s . The a l k a l i f e l d s p a r s w i t h i n t e r m e d i a t e c o m p o s i t i o n v a r y i n t h e i r TL s i g n a l when seen i n d e t a i l . A l l o f them d i f f e r s i g n i f i c a n t l y as a group from t h e end members. However, s e v e r a l i n t e r e s t i n g common f e a t u r e s throw l i g h t on t h e i r o v e r a l l b e h a v i o u r . These f e a t u r e s s u g g e s t a new means f o r i d e n t i f y i n g s t r u c t u r e , w h i c h d i f f e r s from the t r a d i t i o n a l o p t i c a l and X - r a y d i f f r a c t i o n methods. The NTL e m i s s i o n spectrum f o r an i n t e r m e d i a t e a l k a l i f e l d s p a r , a h i g h temperature s a n i d i n e from Mount Soma, I t a l y , (K:Na:Ca 54:43:3) i s shown i n F i g u r e s 2c and 3c. The spectrum i s b r o a d , e x t e n d i n g from about 400 t o 570 nm, a t a temperature o f around 250°C, and i s l i k e l y t o be the composite e f f e c t o f more t h a n one e m i s s i o n band. The 280 C/560 nm peak o b s e r v e d i n h i g h sodium f e l d s p a r s i s e i t h e r absent o r appears v e r y l i t t l e i n t h i s o r i n most o t h e r i n t e r m e d i a t e c o m p o s i t i o n samples. Nor does the 400 nm h i g h - K peak. The samples show TL s e n s i t i v i t y between one t o two o r d e r s o f magnitude l e s s t h a n t h a t o f the end members. The b r o a d band e x t e n d i n g a c r o s s the spectrum i s p r e s e n t t o some degree i n a l l t h e i n t e r m e d i a t e samples s t u d i e d .


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TL and S t r u c t u r e . The examples i n F i g u r e s 2a, b and c t y p i f y the t h r e e main s p e c t r a l t y p e s i n the a l k a l i f e l d s p a r s . As might be e x p e c t e d , f e l d s p a r s o f i n t e r m e d i a t e c o m p o s i t i o n show v a r i o u s c o m b i n a t i o n s o f t h e s e . As an example we c o n s i d e r a moonstone, w h i c h i s a mixed a l k a l i f e l d s p a r . Moonstones d e r i v e t h e i r name from the d i f f u s e r e f l e c t i o n from f i n e , l a m e l l a r , p h y s i c a l l y s e p a r a t e i n t e r g r o w t h s , presumed t o be o f p o t a s s i c and s o d i c end members. F i g u r e s 2d and 3d r e p r e s e n t the 3-D NTL e m i s s i o n o f a moonstone from W i s c o n s i n , USA. The moonstone (K:Na:Ca - 37:58:5) i s d e f i n i t e l y a p h y s i c a l m i x t u r e s i n c e i t owes i t s "moonstone" appearance t o c r y s t a l i n t e r g r o w t h s . Comparison o f the moonstone NTL spectrum w i t h the o t h e r " t y p e " s p e c t r a i n F i g u r e s 2 and 3 r e v e a l s t h a t much o f the l i g h t comes from t h e h i g h - K component ( F i g u r e s 2a and 3 a ) . One can a l s o i d e n t i f y a weaker b r o a d band component e x t e n d i n g a c r o s s the spectrum a t a t e m p e r a t u r e around 250 C. T h i s c o r r e s p o n d s t o a f e l d s p a r o f i n t e r m e d i a t e c o m p o s i t i o n such as i s shown i n F i g u r e s 2c and 3c. There i s no o b v i o u s component c o r r e s p o n d i n g t o the N a - r i c h a l b i t e ( F i g u r e s 2b and 3b) and t h i s suggests t h a t the two i n t e r g r o w t h s a r e o r t h o c l a s e and i n t e r m e d i a t e i n c o m p o s i t i o n r a t h e r t h a n say o r t h o c l a s e and a l b i t e . I n a d d i t i o n , i n t h i s moonstone t h e r e i s an e m i s s i o n around 370 C a t a w a v e l e n g t h o f 590 nm w h i c h i s n o t a c c o u n t e d f o r by the o t h e r "type" spectra. S i n c e the broadband spectrum shown i n F i g u r e s 2c and 3c i s q u i t e d i s t i n c t from those o f the two end members, we i n t e r p r e t i t as from a s i n g l e phase s o l i d s o l u t i o n o f i n t e r m e d i a t e c o m p o s i t i o n . T h i s i s c o n s i s t e n t w i t h what i s known o f the p r o p e r t i e s and provenance o f the i n d i v i d u a l samples, and w i t h i t s c o n s i s t e n t p r e s e n c e i n s p e c t r a f o r most f e l d s p a r s o f i n t e r m e d i a t e c o m p o s i t i o n . A sample from S l i e v e G u l l i o n , I r e l a n d (K:Na:Ca - 4 3 : 5 7 : - ) , d e s c r i b e d as a s a n i d i n e , has e x a c t l y the same s p e c t r a l c h a r a c t e r i s t i c s as the moonstone ( F i g u r e 2d) namely, a m i x t u r e o f h i g h - K and i n t e r m e d i a t e . T h i s sample does n o t have a "moonstone" appearance b u t i s n e v e r t h e l e s s c l e a r l y a s i m i l a r m i x t u r e o f phases e

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b u t presumably the c r y s t a l i n t e r g r o w t h s a r e t o o s m a l l t o show o p t i c a l l y . On the o t h e r hand, US s y n t h e t i c f e l d s p a r s t a n d a r d NBS 99a (K:Na:Ca - 32:57:11) i s e v i d e n t l y a m i x t u r e o f h i g h - K and h i g h Na f e l d s p a r s . T h i s was a s u r p r i s e t o our m i n e r a l o g i s t s b u t t h e e v i d e n c e seems s t r o n g . The mixed phase c h a r a c t e r i s a l s o r e v e a l e d by some f e l d s p a r samples w h i c h a r e c l a s s i f i e d as s a n i d i n e a n d o r t h o c l a s e on the b a s i s o f t h e i r c e l l s t r u c t u r e a n a l y s i s u s i n g Xray d i f f r a c t i o n technique. This s t i l l requires explanation. I t i s i n t e r e s t i n g t o n o t e t h a t t h e o c c a s i o n a l h i g h e r TL s e n s i t i v i t y i n the i n t e r m e d i a t e c o m p o s i t i o n r e g i o n ( o f w h i c h t h e s y n t h e t i c sample 99a i s an example) c o r r e s p o n d s t o t h e degree o f mixed end-member T L s p e c t r a c h a r a c t e r shown b y s u c h samples. Downloaded by PURDUE UNIV on April 6, 2016 | http://pubs.acs.org Publication Date: November 29, 1990 | doi: 10.1021/bk-1990-0415.ch010

Discussion There i s an e x t e n s i v e l i t e r a t u r e on the g r o s s s t r u c t u r e and m i c r o s t r u c t u r e o f f e l d s p a r s and the methods f o r d e t e r m i n i n g them. Three o f the most r e c e n t comprehensive t r e a t m e n t s a t r e v i e w l e v e l a r e found i n r e f e r e n c e s (14) and (15) and i n the c l a s s i c , " F e l d s p a r M i n e r a l s " , by J.V. Smith ( 1 6 ) , now i n i t s second e d i t i o n . O p t i c a l methods, X - r a y d i f f r a c t i o n and e l e c t r o n d i f f r a c t i o n a r e a l l so w e l l - e s t a b l i s h e d t h a t i t h a r d l y seems n e c e s s a r y t o do more t h a n g i v e a b r i e f reminder o f t h e i r p a r t i c u l a r c h a r a c t e r i s t i c s . O p t i c a l methods a r e r a p i d and cheap and f r e q u e n t l y u s e f u l i n o b s e r v a t i o n s o f t w i n n i n g and sample homogeneity and, t o some extent, composition. E l e c t r o n o p t i c a l s t u d i e s have e s t a b l i s h e d t h a t , a p a r t from a few end members and some h i g h t e m p e r a t u r e samples, most f e l d s p a r s c o n s i s t o f two o r more t y p e s o f domains t h a t d i f f e r i n o r i e n t a t i o n o r c o m p o s i t i o n , o r b o t h , on a s c a l e o f 3 t o 100 nm. S i n c e t h i s s c a l e i s s i g n i f i c a n t l y s m a l l e r t h a n t h e w a v e l e n g t h o f l i g h t , o p t i c a l methods n e c e s s a r i l y average o v e r t h e s e s t r u c t u r e s , and t h e i r o p t i c a l p r o p e r t i e s a r e averages o f t h e o p t i c a l p r o p e r t i e s o f i n d i v i d u a l members o f the c o m p o s i t e ( 1 7 ) . On the o t h e r hand, the v e r y h i g h r e s o l u t i o n o f e l e c t r o n o p t i c a l t e c h n i q u e s a l l o w s t h e i d e n t i f i c a t i o n o f d e t a i l on a v e r y much s m a l l e r s c a l e , t o g e t h e r w i t h a n c i l l a r y i n f o r m a t i o n such as p r o v i d e d by m i c r o p r o b e X - r a y e m i s s i o n a n a l y s i s . X - r a y d i f f r a c t i o n h a r d l y needs f u r t h e r comment because o f i t s l o n g - e s t a b l i s h e d c o n t r i b u t i o n t o s t r u c t u r a l s t u d i e s a t t h e atomic l e v e l . The thermoluminescence p r o p e r t i e s o f f e l d s p a r s d e s c r i b e d h e r e s u g g e s t t h a t , p r o p e r l y c a l i b r a t e d , TL e m i s s i o n s p e c t r a can make TL a s i m p l e b u t p o w e r f u l t o o l f o r e s t i m a t i n g l e v e l s o f mixed phases i n f e l d s p a r s . I t appears t h a t the d i f f e r e n c e i n TL s e n s i t i v i t y and the d i f f e r e n c e i n the s p e c t r a are a b l e t o g i v e i n f o r m a t i o n about the c o m p o s i t i o n o f the phases concerned, a t l e a s t t o t h e e x t e n t o f d e t e r m i n i n g b u l k c o m p o s i t i o n and average s t r u c t u r a l s t a t e . I n t h i s r e s p e c t , t h e t e c h n i q u e h a s some s i m i l a r i t i e s t o t h e o p t i c a l methods r e f e r r e d t o above. The TL method d i f f e r s i n t h a t i t i d e n t i f i e s t h e phases from t h e i r s p e c t r a l c h a r a c t e r i s t i c s . F u r t h e r , as an e m i s s i o n r a t h e r t h a n a s c a t t e r i n g phenomenon, t h e s p a c i a l r e s o l u t i o n i s b e t t e r . O p t i c a l m i c r o s c o p y r e v e a l s s t r u c t u r e s down t o , say, 500 nm; X - r a y and e l e c t r o n d i f f r a c t i o n e x t e n d t h i s t o s t r u c t u r e s r o u g h l y a n o r d e r o f magnitude s m a l l e r ; and e l e c t r o n


10. PRESCOTTETAL·


189

microscopy to structures smaller s t i l l . The TL technique suggested here extends to somewhere near the bottom of the size range since the optical emission is related to structures on the atomic scale in lattices which do not need to be ordered to the extent necessary to give coherent X-ray or electron scattering.


Acknowledgments The work was supported by the Australian Research Grants Committee and the Research Grant of the University of Adelaide. RKG expresses his appreciation for support from the University of Adelaide which made possible a visit to the Physical Archaeometry Research Group of that university. Phil Fox provided the analysis for some of the Figures, and John Hutton and Gillian Robertson provided useful comments. Literature Cited 1. McDougall, D.J. In Thermoluminescence of Geological Materials; McDougall, D.J., Ed.; Academic: London, 1968; 527-544. 2. Geake, J.E.; Walker, G.; Telfer, D.J.; Mills, A.A. Trans. Roy. Soc. London 1977, A285, 403-408. 3. Pasternack, E.S.; Levy, P.W. Geological Abstracts with Programs 1978, 10, 468. 4. Marfunin, A.S. Spectroscopy. Luminescence and Radiation Centres in Minerals; Springer-Verlag: Berlin, 1979. 5. Dalal, M.L.; Kirsh, Y.; Rendell, H.M.; Townsend, P.D. Nucl. Tracks and Radiat. Meas. 1988, 14, 57-62. 6. Kirsh, Y.; Townsend, P.D. Nucl. Tracks and Radiat. Meas. 1988, 14, 43-48. 7. Akber, R.A.; Prescott, J.R. Nuclear Tracks 1985, 10, 575-580. 8. Akber, R.A. Materials and Techniques for Thermoluminescence Dating. Ph.D.Thesis, University of Adelaide, Australia, 1986. 9. Huntley, D.J.; Godfrey-Smith, D.I.; Thewalt, M.L.W.; Berger, G.W. Jour. Luminescence 1988, 39, 123-136. 10. McKeever, S.W.S. Thermoluminescence of Solids; Cambridge University Press, 1985. 11. Levy, P.W. PACT 1979, 3, 466-480. 12. Jensen, H.E.; Prescott, J.R. PACT 1982, 6, 542-548. 13. Prescott, J.R.; Akber, R.A.; Jensen, H.E. Applied Optics 1988, 27, 3496-3502. 14. Ribbe, P.H. Ed. Feldspar Mineralogy; Mineralogical Society of America: Washington, DC, 1983. 15. Brown, W.L., Ed.; Feldspars and Feldspathoids; NATO ASI Series C, 137; Riedel: Dordrecht, 1984. 16. Smith, J.V.; Brown, W.L. Feldspar Minerals, 2nd. edition; Springer-Verlag: New York, 1988. 17 Stewart, D.B.; Ribbe P.H. in Feldspar Mineralogy; Ribbe, P.H. Ed.; Mineralogical Society of America: Washington, DC, 1983, 121-137 RECEIVED March 21, 1989


Spectroscopic Characterization of Minerals and Their Surfaces

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