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Deformation twinning in diamond and the identification of the twinning plane
Scripts
METALLURGICA
Vol. 6, pp. 383-386, 1972 P r i n t e d in the U n i t e d States
Pergamon
Press,
DEFORMATION TWINNING IN DIAMOND AND THE IDENTIFICATION OF THE TWINNING PLANE
C .K.R.Varma Depart~,ent of Physics Royal Holloway College (University of London) @
Englefield Green,Surrey,England. 0n leave from C.M.College (University of Bihar),Darbhanga,Bihar,lndia.
(Received M a r c h
13,
1972)
Evidence for deformation twinningindiamond has already been reported (1).Surface discontinuities often appear on natural diamond crystals which on octahedral faces are usually straight and alcng~110~ .Single or multiple and sometimes with trigons strung on them, they girdle the crystals wholly or in part.At high magnification with the crystals suitably tilted, the features show as twin lamellae. As diamonds in nature are likely to be subjected to severe shear stresses at their place of origin (2),it was conjectured (I) that these stresses might have plastically deformed the crystals producing twinning. While the evidence described in reference (I) indicated on the whole that the lamellae constituted a deformation feature,they were sometimes so very thick compared to what are ordinarily produced in crystals by applied stress that doubts lingered (3) whether or not these features could have arisen in growth or dissolution.We report here eVidence which would confirm that the lamellae arise in deformation and that the twinning plane is very possibly 1111 \. Figure I shows twin lamellae on the curved surface of a broken (broken in nature) piece of diamond and figure 2 shows its opposite side.The vertical traces on the broken side correspond one to one with the twins imfigure I implying that they are not surface features but deformation traces that run through the body of the crystal.
383
Inc
384
DEFORMATION
TWINNING
IN DIAMOND
Vol.
This we have confirmed by cleaving diamonds bearing deformation lamellae. Figure 2 shows that deformation traces displace sharply as they meet cleavage steps indicating that the twinning plane is not normal to the cleavage plane.Traces similarly displace as they
descend i n t o t r i t o n p i t s on o c t a h e d r a l f a c e s . F i g u r e s 3 and 4 a r e examples. We have i n a number o f c a s e s measured the d i s p l a c e m e n t of the t r a c e and the COZTespondin~ d i f f e r e n c e i n s u r f a c e l e v e l s as the t r a c e meets a s t e p or descends into a pit.The ratio of level difference to displacement gives fan,where ~ is the angle that the twinning plane makes with the natural or cleaved surface. Natural surfaces showing trigons with relatively little topographic teller,as for example as in figures 3 and 4,are tolerably
~111 f
.The favoured and therefore most predominant cleavage
plane in a crystal is determined by the number and strength of the bonds across individual planes and in diamond it is well known (4 - 6) that
t h i s p l a n e of minimum s u r f a c e energy i s ~ 111~ .We t h e r e f o r e assume t h a t t h e c l e a v a g e p l a n e l i k e t h a t i n f i g u r e 2" i s "very n e a r l y ~1111.The v a l u e of~cbtained
f r o m measurements,though somewhat v a r y i n g , w a s i n most cases
n e a r to 70°.We t h e r e f o r e conclude t h a t the twinning p l a n e i s ~ 1111
e
Churchma~ et al (7) found that in silicon, ~ermanlum,gallium antlmonide and indium antlmonide (all which have the We have so far come across no indication for this in diamond.
References 1.C.K.R.Var~,Acta Met.18,1113 (1970). 2.F.C.Fzmnk,Prooeedin~s of the Intex~aational Diamond Conference Oxford (1966),p.119.IDlB,London
(1967).
3.G.S.Woods,Phil.~g.23,475 (1971). 4.S.Ramaseshan,Proc.lndian Acad.Sci.24,114 (1946). 5.C.A.Coulson,Valence,p.185.0xford University Press (1961). 6.Y.P.Bowden and D.Tabor,Physlcal Properties of Diamond edited by R.Berman,p.186.Clarendon Press,0xford (1965). 7.A.T.Churchman,G.A.Geach and J.Winton,Proc.R.Soc.A 238,194 (1956).
6, No.
5
Vol.
6, No.
5
DEFORMATION
TWINNING
IN D I A M O N D
Fig.l: Twin lamellae on a broken piece of diamond.(X 100)
Fig.2: The traces on the broken side correspond one to one with the twins. (X I 00)
38S
386
DEFORMATION
TWINNING
F±~.3 (x I~o)
IN DIAMOND
Vol.
z±¢.4 (x I~o)
Deformation t r a c e s d i s p l a c e as they descend i n t o t r i t o n p i t s .
6, No.
METALLURGICA
Vol. 6, pp. 383-386, 1972 P r i n t e d in the U n i t e d States
Pergamon
Press,
DEFORMATION TWINNING IN DIAMOND AND THE IDENTIFICATION OF THE TWINNING PLANE
C .K.R.Varma Depart~,ent of Physics Royal Holloway College (University of London) @
Englefield Green,Surrey,England. 0n leave from C.M.College (University of Bihar),Darbhanga,Bihar,lndia.
(Received M a r c h
13,
1972)
Evidence for deformation twinningindiamond has already been reported (1).Surface discontinuities often appear on natural diamond crystals which on octahedral faces are usually straight and alcng~110~ .Single or multiple and sometimes with trigons strung on them, they girdle the crystals wholly or in part.At high magnification with the crystals suitably tilted, the features show as twin lamellae. As diamonds in nature are likely to be subjected to severe shear stresses at their place of origin (2),it was conjectured (I) that these stresses might have plastically deformed the crystals producing twinning. While the evidence described in reference (I) indicated on the whole that the lamellae constituted a deformation feature,they were sometimes so very thick compared to what are ordinarily produced in crystals by applied stress that doubts lingered (3) whether or not these features could have arisen in growth or dissolution.We report here eVidence which would confirm that the lamellae arise in deformation and that the twinning plane is very possibly 1111 \. Figure I shows twin lamellae on the curved surface of a broken (broken in nature) piece of diamond and figure 2 shows its opposite side.The vertical traces on the broken side correspond one to one with the twins imfigure I implying that they are not surface features but deformation traces that run through the body of the crystal.
383
Inc
384
DEFORMATION
TWINNING
IN DIAMOND
Vol.
This we have confirmed by cleaving diamonds bearing deformation lamellae. Figure 2 shows that deformation traces displace sharply as they meet cleavage steps indicating that the twinning plane is not normal to the cleavage plane.Traces similarly displace as they
descend i n t o t r i t o n p i t s on o c t a h e d r a l f a c e s . F i g u r e s 3 and 4 a r e examples. We have i n a number o f c a s e s measured the d i s p l a c e m e n t of the t r a c e and the COZTespondin~ d i f f e r e n c e i n s u r f a c e l e v e l s as the t r a c e meets a s t e p or descends into a pit.The ratio of level difference to displacement gives fan,where ~ is the angle that the twinning plane makes with the natural or cleaved surface. Natural surfaces showing trigons with relatively little topographic teller,as for example as in figures 3 and 4,are tolerably
~111 f
.The favoured and therefore most predominant cleavage
plane in a crystal is determined by the number and strength of the bonds across individual planes and in diamond it is well known (4 - 6) that
t h i s p l a n e of minimum s u r f a c e energy i s ~ 111~ .We t h e r e f o r e assume t h a t t h e c l e a v a g e p l a n e l i k e t h a t i n f i g u r e 2" i s "very n e a r l y ~1111.The v a l u e of~cbtained
f r o m measurements,though somewhat v a r y i n g , w a s i n most cases
n e a r to 70°.We t h e r e f o r e conclude t h a t the twinning p l a n e i s ~ 1111
e
Churchma~ et al (7) found that in silicon, ~ermanlum,gallium antlmonide and indium antlmonide (all which have the We have so far come across no indication for this in diamond.
References 1.C.K.R.Var~,Acta Met.18,1113 (1970). 2.F.C.Fzmnk,Prooeedin~s of the Intex~aational Diamond Conference Oxford (1966),p.119.IDlB,London
(1967).
3.G.S.Woods,Phil.~g.23,475 (1971). 4.S.Ramaseshan,Proc.lndian Acad.Sci.24,114 (1946). 5.C.A.Coulson,Valence,p.185.0xford University Press (1961). 6.Y.P.Bowden and D.Tabor,Physlcal Properties of Diamond edited by R.Berman,p.186.Clarendon Press,0xford (1965). 7.A.T.Churchman,G.A.Geach and J.Winton,Proc.R.Soc.A 238,194 (1956).
6, No.
5
Vol.
6, No.
5
DEFORMATION
TWINNING
IN D I A M O N D
Fig.l: Twin lamellae on a broken piece of diamond.(X 100)
Fig.2: The traces on the broken side correspond one to one with the twins. (X I 00)
38S
386
DEFORMATION
TWINNING
F±~.3 (x I~o)
IN DIAMOND
Vol.
z±¢.4 (x I~o)
Deformation t r a c e s d i s p l a c e as they descend i n t o t r i t o n p i t s .
6, No.