Abstract
The generation of both Brazil and Dauphiné twins is triggered by strain fields associated with the fluctuation of growth parameters when solid inclusions of goethite (?) are precipitated on to a growth surface. Brazil twins are generated either directly from solid inclusions of smaller size or dislocations originating therefrom, whereas Dauphiné twins are generated only directly from solid inclusions of larger size. Precipitation of polymerized embryonic particles of SiO2 on the surface of solid inclusions is considered to be responsible for the generation of Brazil twins, whereas for Dauphiné twins it is necessary that embryonic particles precipitated in twin orientation on the surface of solid inclusions grow beyond a critical size.
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Sunagawa, I., Taijing, L. & Balitsky, V.S. Generation of Brazil and Dauphiné twins in synthetic amethysts. Phys Chem Minerals 17, 320–325 (1990). https://doi.org/10.1007/BF00200127
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DOI: https://doi.org/10.1007/BF00200127