MÖSSBAUER STUDY OF NATURAL GLASSES : LIPARI AND TEOTIHUACAN OBSIDIANS

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MÖSSBAUER STUDY OF NATURAL GLASSES : LIPARI AND TEOTIHUACAN OBSIDIANS

F. Chavez-Rivas, J. Régnard, J. Chappert

To cite this version:

F. Chavez-Rivas, J. Régnard, J. Chappert. MÖSSBAUER STUDY OF NATURAL GLASSES : LI-

PARI AND TEOTIHUACAN OBSIDIANS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-

275-C1-276. �10.1051/jphyscol:1980196�. �jpa-00219789�

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JOURNAL DE PHYSIQUE Colloque C1, suppl6ment au n O 1 , Tome 41, janvier 1980, page C1-275

&SBAUER SNDY OF NATURAL GLASSES

:

LIPARI AND TEOTIHUACAN OBSIDIANS F. Chavez-Rivas, J . R . R e g n a r d and J. C h a p p e r t

Centre drEtudes NucZe'aires, D.R.F./Laboratoire drInteractions Hyperfines, 85 X

-

³⁸⁰⁴¹

Grenob Ze Ce'dex, France.

M8ssbauer s t u d i e s o f glasses c o n t a i n i n g i r o n have been performed e s s e n t i a l l y on s y n t h e t i c ill asses, based on phosphates, a1 k a l i ne s i l i c a t e s o r b o r i c oxides. I n most cases the percentage i n weight o f i r o n was g r e a t e r than 5 %. A comprehen- s i v e review of these s t u d i e s has been given by Coey [l] and K u r k j i a n [2]. Here we r e p o r t t h e pre 1 im i nary r e s u l t s o f t h e c h a r a c t e r i z a t i o n of two n a t u r a l v o l c a n i c glasses, t h e b l a c k obsidians from LIPARI ( i s l a n d o f southern I t a l y ) and from TEOTIHUACAN ( c e n t r a l p a r t o f Mexico)

.

^These

obsidians a r e c h a r a c t e r i z e d by a low content i n i r o n oxides ( l e s s than 2.2 % i n weight). I n t h i s work we used v a r i o u s techniques such as X-fluores- cence, X-ray d i f f r a c t i o n , MSssbauer spectroscopy and magnetization measurements.

The compositions o f these two obsidians de- t e r m i ned by X - f 1 uorescence and mass spectrometry on d r y m a t e r i a l s are g i v e n i n t a b l e I. The percen- tages o f i r o n oxides a r e o n l y 1.5 % and 2.15 % f o r t h e LIPARI and TEOTIHUACAN obsidians respec- t i v e l y . We a l s o n o t e an i m p o r t a n t p r o p o r t i o n of amorphous s i l i c a ( l a r g e r than 70 %) and t h e presen- ce o f a t l e a s t t e n mineral oxides. X-ray d i f f r a c - t i o n p a t t e r n s show a s i n g l e broad peak a t 28 = 23", c h a r a c t e r i s t i c o f an amorphous s t a t e . No t r a c e of c r y s t a l l i n e phase was detected f o r 28 ranging from 10" t o 80".

TEOTIHUACAN 73.7

13.35 0.07 3.98 5.10 0.7

: < 0.1

( I r o n oxides : 1.5

( MnO 645(ppm)

( B2°3 : < 1 OOO(ppm)

!

^'2'5 ~ O ( P P ~ )

Table I

-

Chemical composition o f two obsidians ( i n % except when i n d i c a t e d ) .

The samples used i n t h e MSssbauer experiments were e i t h e r s l i c e s c u t i n t h e b u l k glasses o r f i n e powders ( g r a i n s i z e o f about one micron)

.

^No

s i g n i f i c a n t d i f f e r e n c e was observed between these two k i n d s o f samples, c o n f i r m i n g t h e amorphous s t a t e o f t h e m a t e r i a l s .

t .

^t ^. ^t^.^A^- ^-

-31.0 -5.5 0.0 5.5 11.0

,

^brn-GC,TY

Nx,si

The s p e c t r a o f t h e LIPARI o b s i d i a n a t 300 K, 77 K and 4.2 K appear e s s e n t i a l l y as a broad asym- m e t r i c a l d o u b l e t ( f i g . 1). Considering r e a l i s t i c values o f isomer s h i f t s and quadrupole s p l i t t i n g s u s u a l l y found i n s i m i l a r systems, t h e b e s t - f i t o f t h e s p e c t r a a t 300 K and 77 K i n d i c a t e s t h a t they r e s u l t o f t h e s u p e r p o s i t i o n o f two quadrupole doublets a t t r i b u t e d t o Fez+ (92

+

2 %) and Fe3+

( 8

+

²

¹⁾

charge s t a t e s whose h y p e r f i n e parameters a r e g i v e n i n Table 11. The asymmetry o f t h e doublets i s probably due t o a d i s t r i b u t i o n o f quadrupole i n t e r a c t i o n s and isomer s h i f t s . A t 4.2 K t h e ~ e d o u b l e t disappears w h i l e a weak and ~ + broad magnetic p a t t e r n (average Hhf = 500 kOe), r e p r e s e n t i n g approximately 13 % of t h e t o t a l

i n t e n s i t y becomes apparent ( f i g . 1). L e t us remark

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980196

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C1-276 JOURNAL DE PHYSIQUE

t h a t a general f e a t u r e o f these s p e c t r a i s t h e i m p o r t a n t w i d t h s o f t h e i n d i v i d u a l h y p e r f i n e l i n e s which extend from 0.7 mm t o 1.4 mm/s, i.e. much

l a r g e r than those observed i n t h e c r y s t a l l i n e systems. This broadening i s t y p i c a l o f €he t o p o l o - g i c a l and 'chemical d i s o r d e r s o f t h e i r o n envi ron- ment i n t h e g l a s s y s t a t e .

T Charge Isomer Quadrupole I n t e n s i t y (K) s t a t e shift,, s p l i t t i n g ( % )

(mm/s ) ( m / s )

..

With r e s p e c t t o i r o n metal.

.*., ..,.

The parameters o f t h e magnetic p a t t e r n are n o t i n d i cated.

Table I 1

-

LIPARI o b s i d i a n

' OBSIDIAN

Figure 2

A s i m i l a r a n a l y s i s was c a r r i e d o u t f o r t h e TEOTIHUACAN o b s i d i a n ( f i g . 2). There a s i g n i f i c a n t d i f f e r e n c e i s observed ( t a b l e 11). The amount of

~ e (55 ~ +2 3 % a t 300 K) i s much l a r g e r t h a n . i n the LIPARI o b s i d i a n ( 8 %). A l s o a weak magnetic S t r u c t u r e a l r e a d y observed a t 77 K (15 X ) becomes very pronounced a t 4.2 K (26 %, w i t h Hhf = 520 kOe).

T Charge Isomer Quadrupole I n t e n s i t y

(K) s t a t e shift:: split-iiing (%)

(mm/s ) (mm/s )

'' With r e s p e c t t o i r o n metal.

..a,

# . , .

The parameters of t h e magnetic p a t t e r n are n o t i n d i c a t e d .

Table I 1 1

-

TEOTIHUACAN o b s i d i a n

Magnetization measurements a r e a l s o very use- f u l f o r t h e c h a r a c t e r i z a t i o n o f such m a t e r i a l s . F i r s t we observed t h a t t h e powder o f TEOTIHUACAN o b s i d i a n was s t r o n g l y a t t r a c t e d . b y a small pema- n e n t magnet even a t room temperature. We then performed s t a t i c magnetic measurements i n h i g h magnetic f i e l d s and a t low temperatures a t t h e Service N a t i o n a l des Champs Intenses i n Grenoble.

No magnetic f i e l d was a p p l i e d on t h e samples p r i o r o r d u r i n g t h e c o o l i n g c y c l e . A t 4.2 K t h e e x t e r n a l f i e l d was g r a d u a l l y increased up t o a maximum of 150 kOe, and t h e corresponding magneti z a t i o n !as measured. kte n o t i c e d t h e 1 ack o f h y s t e r e s i s loop, t h e absence o f remanent magneti- z a t i o n when t h e e x t e r n a l f i e l d i s removed. The s a t u r a t i o n magnetizations MS per gram o f o b s i d i a n g l a s s a r e 3.6 u.e.m. and 6.94 u.e.m. f o r t h e LIPARI and TEOTIHUACAN obsidians r e s p e c t i v e l y . These values a r e w i t h i n t h e expected range f o r magnetic m a t e r i a l s c o n t a i n i n g p a r t i cules o f Fe304 (27 u.e.m./gr f o r b u l k magnetite a t 300 K 133).

Je conclude t h a t these o b s i d i a n n a t u r a l glasses c o n t a i n free ~e'+ and ~ e i o n s i n various amounts ~ + and a l s o small Fe304 amorphous p a r t i c l e s , whose average s i z e i s l i k e l y t o be l a r g e r i n t h e TEOTIHUACAN obsidian.

Rebaenca

[I] KURKJIAN, C.R., J. Non Cryst. S o l i d s

3

⁽¹⁹⁷⁰⁾

157.

[21 COEY, J.M.D., J. Physique

3

(1974) C6-89.

131 KRUPYANSKII Yu.F. and SUZDALEV I.P., J. Physique

-

35 (1974) C6-407.