Electronic Resource
[S.l.]
:
International Union of Crystallography (IUCr)
Acta crystallographica
25 (1969), S. 578-580
ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
A replication electron microscopy study of etched fracture surfaces of opal revealed four distinctive patterns of packing of the constituent SiO2 spheres. These patterns could be accounted for by consideration of appropriate stacking faults or modifications in a cubic closest packed structure. These were (1) intrinsic stacking faults (2) extrinsic stacking faults (3) twinning and (4) rhombohedral polytypism. The success in predicting some of the observed packing patterns by assuming stacking modifications of a cubic closest packed structure indicates the existence of a basic, though frequently faulted, f.c.c. opal structure. Screw dislocation-spiral growth is proposed as a possible mechanism for explaining the occurrence of the ordered opal structures.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739469001227
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