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3.14 Polycrystalline Materials • 85
Figure 3.19 A garnet single crystal that was found in Tongbei, Fujian Province, China.
(Photograph courtesy of Irocks.com, Megan Foreman photo.)
(a) (b)
(c) (d)
Figure 3.20 Schematic diagrams of the various stages in the solidification of a polycrystalline material; the square
grids depict unit cells. (a) Small crystallite nuclei. (b) Growth of the crystallites; the obstruction of some grains that
are adjacent to one another is also shown. (c) Upon completion of solidification, grains having irregular shapes have
formed. (d) The grain structure as it would appear under the microscope; dark lines are the grain boundaries.
(Adapted from W. Rosenhain, An Introduction to the Study of Physical Metallurgy, 2nd edition, Constable & Company Ltd.,
London, 1915.)
