luster
in white pearls and for the fact that the outer skins of very lustrous
pearls are usually very thin also. Similar conditions exist in colored
pearls, though the presence of a pigment makes them less noticeable.
The skins of the haliotis pearl, which separate easily, usually show
remarkable luster on the inner surface. Sometimes the nucleus is
surrounded by a confused mass without apparent concentric markings, as
though it had been enveloped in nacre which had solidified while
stationary, or the first deposit shows the concentric skin arrangement
at one segment of the circle only; followed by layers which appear in
the depressions of the mass and are continued until they finally
include the whole pearl. These layers are usually very thin, and the
partial or segmentary layer formation is quite common in the early
stages of the pearl's growth. At that period the concentric lines are
also irregular, and in many cases where the curve is true, they extend
about one quarter of the circumference only, another concentric skin
being lapped on the ends, as though the globular skin had been formed
in sections.
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