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Black Coral
This consists of the skeletons of polyp colonies,
mainly of the genera Gorgonia, Eunicella, Gerardia, and Parantipathes;
but unlike those that make up red, pink, and blue coral, these
skeletal remains are of a horny nature, no calcic.
Appearance The color is black, but sometimes
has minute, short, brownish yellow, slightly translucent streaks.
It can acquire quite good luster if polished, but this will
be of a horny character, similar to that of some plastics.
It is usec in cylindrical pieces which are drilled along the
axis or horizontally to it, as necklace beads. It can be bent
if heated and made into bangles. Cheap rings, carved items
and figurines up to ten centimeters tall are also made from
larger pieces.
Distinctive features If cut crossways to
the axis, the characteristic concentric rings, like those
of tree trunks are visible. These sometimes have marked discontinuities
between one and the other, almost as though they were becoming
detached. Faint radial structures and thin longitudinal structures,
yellowish brown in color and slightly translucent, may also
be visible. Sometimes, these limitec: areas of yellow-brown
translucency show small protuberances on the underlying surface,
as would have beer present on the outer surface had it not
been polished (or black coral of the genus Parantipathes).
It is no use testinc black coral with hydrochloric acid, as
it does not contain calcium carbonate; but it should be remembered
that the density is about 1.36 g/cm3, which is much lower
than that of red and pink corals. Due to its proteinaceous
character black coral emits a smell of burning horn if touched
with a piece of red-hot wire. It is warm to the touch, like
plastic has a relatively low hardness of between 2 and 3,
and is slightly elastic.
Occurrence It is gathered near the Hawaiian
islands, ir the Great Barrier Reef of Australia, in the Red
Sea, on the west coast of Africa, the Antilles and, occasionally,
in the Mediterranean.
Value Distinctly low, much lower than that
of the main types of coral. As an ornament it is characteristic
of many different cultures, but in the West it is mainly regarded
as a curiosity, although appreciable quantities were seen
on the market a few years ago.
Simulants It does not appear, at present,
to be imitated
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