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Clays and Clay M inerals

Vol. 22 pp. 309-310. Pergamon Press 1974. Printe d in Great Britain

R E P L Y T O : C O M M E N T S O N A N E X P A N S I B L E M I N E R A L

H A V I N G H I G H R E H Y D R A T I O N A B IL IT Y

R e c e i v e d 6 F e b r u a r y 1974)

I n h i s C o m m e n t s , C o l e h a s p o i n t e d o u t t h a t h e a t i n g t i m e o f

1 h r w as s ho r t . I n th i s r ega rd , t he in f luence o f pa r t i c l e s iz e

s h o u l d b e c o n s id e r e d . O u r e x p e r i m e n t s u s ed a s a m p l e p a r -

t ic le s iz e < 2 /~m and the hea t ing was d one on a ve ry th in

f i lm on the g la ss sl ide . W e tho ugh t tha t I h r was long enou gh

to expe l a l l i n t e r l aye r wa te r . We have reexamined the

s ample and have found tha t i t ha s h igh capac i ty fo r

rehy dra t ion even a f te r hea t ing to a t l e a s t 830~ fo r 5 h r .

C o le s t a t e s tha t c e r t a in ve rm icu l i t es have a h igh capac i ty

to rehydra te s o long a s they con ta in s ome hydroxy l wa te r .

I ag ree w i th h im, bu t c e r t a in o the r ve rmicu l i t e s w i l l no t

rehydra te . I won de r i f i t is c e r t a in tha t t he re i s a r e l a t ion

be tween ex i s t ence o f hydroxy l wa te r and rehydra t ion .

R ecen t s tud ie s have conf i rmed tha t c e r t a in regu la r ly in t e r -

s t ra t i f i ed mine ra l s have h igh rehydra t ion ab i l i t y . Howeve r ,

de s p i t e th i s h igh rehydra t ion capac i ty the dehydroxy la t ion

p e a k s i n t h ei r D T A c u r v e s d o n o t o c c u r a t h i g h t e m p e r a t u r e

(C o le and Hos k ing , 1957 ; B r ind ley and Sanda lak i , 1963 ;

T o m i t a

e t a l . ,

1969 ; To mi ta an d Do zono , 1973 ; To mi ta

e t

a l . , 1 97 4) . M a n y m o n t m o r i l l o n i t e s a n d a l l h y d r a t e d h a l lo y -

s i te s do no t r ehydra te a f t e r hea t ing to c e r t a in t emp e ra tu re s

des p i t e r e t a in ing s ome hydroxy l wa te r . I s ve rmicu l i t e the

on ly m ine ra l wh ich wi ll r ehydra te a f t e r hea t ing un t i l a l l hy -

dro xyl wa ter is lost ?.

Wa lke r and C o le (1957) and Wa lke r (1961) repor t ed tha t

B a tav i t e does no t lo s e the l a s t t r a ce o f in t e r l aye r wa te r un t i l

abou t 800~C . In h i s C omments , C o le exp la ins tha t i t migh t

be expec ted tha t B a tav i t e wou ld rehydra te a f t e r hea t ing to

800~ Al th oug h in the i r fo rmer pub l i c a t io ns i t was no t

c l ea r ly me n t ione d tha t B a tav i t e pos s e s s ed s uch capac i ty , i n

the C om me nts i t is s t a t ed tha t B a tav i t e does pos s e ss a h igh

r e h y d r a t i o n c a p a c i t y . W h e n t h e m i n e r a l w a s a l l o w e d t o

rehyd ra te in a i r af t e r hea t ing to 800~ a 14 .2A re f l e c tion

typ ica l o f the un hea te d min e ra l was pa r t i a lly recove red . An

in te r s t ra t if i ed mine ra l f rom Iw a to inves t iga ted by Tom i ta

and Dozono (1973) comple te ly rehydra ted a f t e r hea t ing to

800~

S o m e r e a s o n s a r e c o n s i d e r e d f o r h i g h r e h y d r a t i o n c a p a -

c ity. As po in ted ou t by Gr anq u i s t an d Ken nedy (1967) , f luo r -

ide in hydroxy l s i t e s enhances the wa te r s o rp t ion capac i ty .

W r i g h t

e t a l .

(1972) sugges ted, for the same c lay s tudied by

G r a n q u i s t a n d K e n n e d y , t h a t t h e t h e r m a l l y a c t i v a te d s u b -

s t ance had p ro tons in the t e t rahe dra l vacanc ie s o f the oc ta -

hed ra l l aye r . In h i s C omm ents , C o le conc luded th a t t he

g r e a t e r r e h y d r a t i o n c a p a c i t y o f B a t a v it e a n d L l a n o v e r m i c u -

l i te ove r the ma te r i a l f rom Wes t C hes te r m igh t be due to the

fac t t ha t t he fo rm er con ta in no i ron in the oc tahedra l l aye r.

I t h ink th i s l a ck o f i ron i s one o f the rea s ons . Fo r example ,

t h e d e h y d r o x y l a t i o n p e a k o f n o n t r o n i t e o c c u r s a t a l o w e r

temp e ra tu re t han in the ca s e o f i ron - f ree ana logs .

T h e r e h y d r a t i o n o f m o n t m o r i l l o n i t e a f t e r h e a t i n g t o

t emp e ra tu re s up to 1000~ has been inves t iga ted by Gr im

and B rad ley (1948) and by Hi l l (1953) . They conc lud ed tha t

a f t e r p rehe a t ing to 800~ d ioe tahed ra l s mec t it e s do n o t

s how apprec iab le rehydra t ion . DTA curves o f s ome t r ioc ta -

hed ra l s mec t i t e s g ive dehyd roxy la t ion peaks a t h igh t em-

pe ra tu re s . Sapon i t e f rom Kruge rs dorp , Trans vaa l , Sou th

Afr i ca dehydroxy la t e s be tween 800 and 900~ and C a l i fo r-

n ia hec to r i t e a t abo u t 800~ (Schm id t and H eys tek , 1953).

S o m e s m e c t i t e s h a v i n g h i g h a m o u n t s o f M g i o n s i n t h e

oc tahedra l l aye r migh t be expec ted the re fo re to have h igh

rehydra t ion capac i ty . Unfo r tuna te ly , I cou ld no t ob ta in

pure s pec imens o f such k inds , and cou ld n o t inves t iga te

the i r c apac i ty to rehydra te . The p rob lem s a re l e ft fo r fu tu re

s tudy.

I s uppos e tha t one o f the m a in rea s ons fo r h igh

rehydra t ion capac i ty may be due to the mine ra l s t ruc tu re .

B a tav i t e ha s an AI :S i r a t io o f 1 :3 in i t s t e t rahedra l l aye r

(We is s and Hofmann , 1951) ; L lano ve rmicu l i t e a co r re -

s pond ing AI : S i r a t io o f 1 :2 (va n O lphen , 1965). C e r t a in in -

t e r s t ra t i f i ed mine ra l s w i th h igh rehydra t ion ab i l i t y have

fa i rly h igh s ubs t i tu t ion o f AI fo r S i t e t rahedra l ly (Tom i ta

e t

a l . ,

1 96 9; T o m i t a a n d D o z o n o , 1 97 3; T o m i t a a n d D 6 z o n o ,

1974) . I have found tha t a Tos ud i t e inves t iga ted by

Kanaoka (1968) ha s a h igh rehydra t ion capac i ty and a l s o

has a fa i rly h igh s ubs t i tu t ion o f A l fo r S i. Thus , s pec imens

hav ing h igh t e t rahedra l s ubs t i tu t ion o f AI fo r S i s eem to

have th i s r ehyd ra t ion ab i l i t y .

According to Tomita and Sudo (1968a, b) , a 2Mr ser ic i te ,

w h i c h h a d b e e n h e a t e d t o d e h y d r o x y l a t i o n te m p e r a t u r e s

(650-950~ was con verte d in to a regular ly in ters t ra t i f ied

s t ruc tu re by bo i l ing in a c id s o lu t ion fo r a f ew minu te s .

R e h y d r a t i o n a n d r e h y d o x y l a t io n t h e r e f o re o c c u r r e d i n t h e

hea ted s e r i c i t e unde r re l a t ive ly mi ld cond i t ions . Why i s i t

t h a t r e h y d r a t i o n a n d r e h y d r o x y l a t i o n o c c u r s o e a s i l y i n

hea ted s e r i c i t e ? Tomi ta and Dozono (1972) s ucceeded in

fo rming a regu la r ly in t e r s t ra t i f i ed mine ra l f rom dehydroxy -

l a t ed 2M t s e r ic i te by ex t rac t ion o f K ion w i th s od ium

t e t r a p h e n y l b o r o n a t r o o m t e m p e r a t u r e a n d p r e ss u r e. H e r e ,

r e h y d r a t i o n a n d r e h y d r o x y l a t i o n a g a i n o c c u r r e d i n t h e

dehydrox y la t ed s e ri ci te , t h i s t ime d u r ing ex t rac t ion o f K

ion f rom in te r laye rs .

We is s enbe rg pho to g rap hs o f s ome ve rm icu l i t es g ive d i f-

fus e s po t s , wh ich can be cons ide red ev idence tha t t he s e ve r -

micu l i t e s have d i s to r t ed s t ruc tu re s . Th i s d i s to r t ion may be

due pa r t ly to t e t rahedra l s ubs t i tu t ion o f AI fo r S i . Hea ted

s e r i c i t e s a l s o have d i s to r t ed s t ruc tu re s (Tomi ta and Sudo ,

1968b). Thes e d i s to r t ed s t ruc tu re s s eem to p lay an impor -

t a n t r o l e i n r e h y d r a t i o n a n d r e h y d r o x y l at i o n .

R ecen t ly , Tomi ta (1974) repor t ed tha t t he rehydra t ion

and rehydroxy la t ion p rope r t i e s o f r e c to r i t e a re s imi l a r to

thos e o f 2M s er ic it es . W hy a re the s e p rope r t i e s o f 2M s e r i-

c i tes d ifferent f rom lM seric ites? W e repo rted an in ters t ra t i -

f led mine ra l hav ing h igh rehydra t io n ab i li t y . We thou gh t the

p h e n o m e n o n w o u l d b e h e l p fu l f o r i n t e rp r e t a t i o n o f t h e o r i -

g in o f in t e r s t ra t i f i ed mine ra l s ; i t s e ems to be equa l ly pe r -

t i n e n t t o d i s c u s s i o n o f t h e p r o b l e m s o f h i g h r e h y d r a t i o n

capaci ty .

P u r e s p e c im e n s h a v i n g h i g h r e h y d r a t i o n a b i l it y s h o u l d b e

found in the near future . Studies on such specif iaens should

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310 Notes

establ i sh the reasons for the observed high rehydra t ion and

rehydroxyla t ion capaci ty .

The wri te r expresses his apprec ia t ion to Dr . W. F. Cole

for his Comments.

Institute of Earth Sciences

Kagoshima University

Kagoshima Japan

KATSUTOSHITOMITA

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