Growth Mechanisms, Polytypism, and Real Structure
of Kaolinite Microcrystals

N. D. Samotoin

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences,
Staromonetny per. 35, Moscow, 119017 Russia

e-mail: samnik@igem.ru

Received June 28, 2007; in final form, May 5, 2008

Abstract—The mechanisms of growth of kaolinite microcrystals (0.1–5.0 µm in size) at deposits related to the
eluvial weathering crust, as well as to the low-temperature and medium-temperature hydrothermal processes of
transformations of minerals in different rocks in Russia, Kazakhstan, Ukraine, Czechia, Vietnam, India, Cuba,
and Madagascar, are investigated using transmission electron microscopy and vacuum decoration with gold. It
is established that kaolinite microcrystals grow according to two mechanisms: the mechanism of periodic for-
mation of two-dimensional nuclei and the mechanism of spiral growth. The spiral growth of kaolinite microc-
rystals is dominant and occurs on steps of screw dislocations that differ in sign and magnitude of the Burgers
vector along the c axis. The layered growth of kaolinite originates from a widespread source in the form of a
step between polar (+ and –) dislocations, i.e., a growth analogue of the Frank–Read dislocation source. The
density of growth screw dislocations varies over a wide range and can be as high as ~10⁹ cm². Layered stepped
kaolinite growth pyramids for all mechanisms of growth on the (001) face of kaolinite exhibit the main features
of the triclinic 1Tc and real structures of this mineral.

PACS numbers: 68.37.Lp, 81.10.Aj

DOI: 10.1134/S1063774508050271

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