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Red Coral
The oldest known findings of red coral date
from the Me sopotamian civilization, i.e. from about 3000
BC. For cer turies, this was the coral par excellence, and
at the time c Pliny the Elder it was apparently much appreciated
in India even more than in Europe. The name is derived from
th• Latin corallium, related to the Greek korallion.
Appearance The red coral from the Mediterranea(Corallium
rubrum) has very faint concentric rings. It is easier to see
the longitudinal structures. The type from thseas near Japan
has more clearly visible organic struc tures. The thin branches
were and still are polishec pierced, and threaded, unaltered,
into necklaces. Large pieces are cut into spherical or faceted
necklace beads pear shapes for pendant jewelry, or cabochons.
This cora is very compact and easily acquires a good polish,
a, though this may deteriorate in time as the material is
nc* very durable. It is also used for carved pieces and small
ficurines, in both oriental and western art styles.
The most highly prized varieties of coral are those that arF
a uniform, strong, bright red. Specimens that are too lighor
too dark, or have an orange tinge or unevenly distribw color,
are less valuable. Some basically red Japane corals have a
white axial portion. This is, of course, garded as a defect,
where it is not eliminated in the cutt process.
Distinctive features Two basic facts must
be reme bered in distinguishing coral from its imitations:
1) The specimen should have the organic structure ch - acterlstic
of coral;
2) On contact with a drop of hydrochloric acid (the reac available
muriatic acid), the piece should display the strceffervescence
characteristic of calcite.
The most frequent imitations are of glass. These have Ic gitudinal
striations similar to those of coral, but do not rea: to hydrochloric
acid. Another common simulant is ma, from a compact, artificial
agglomerate mainly of calciwhich lacks any trace of organic
structure. As mentione the hardness is about 3.5, therefore
well below that glass. The organic substance in coral also
gives it vFgood tenacity, far superior to that of the constituent
miner alone. Because of its organic content, the density var
- quite widely, but is usually about 2.60-2.66 g/cm3.
Occurrence Red coral is gathered
in the Mediterrane.., (mainly near Sardinia and Sicily), the
Eastern Mediterra ean, the Red Sea, and the seas around Japan.
Value When made into polished and/or faceted
neclace beads, it has roughly the same value as that of certa
prized ornamental stones, such as good quality turquoi~ and
lapis lazuli, The color, homogeneity of each pie (individually
and as part of a necklace) and polish are ve important. When
the coral is made into carved pieces ar figurines, the quality
of the work is obviously very impc tant. Furthermore, it should
be remembered that larc pieces are hard to find.
Simulants and synthetics Very small pieces
of coral - branching twigs are imitated by special glass which
sim lates the typical longitudinal structures; but clearly
fuse surfaces, the presence of air bubbles, and immunity to
atack from hydrochloric acid uncover these imitations qui•easily,
especially if they are viewed through a lens or bit ocular
microscope. Nowadays, a coral-colored agglome, ate consisting
mainly of calcite and called synthetic coral - also manufactured.
This reacts to hydrochloric acid in th same way as true coral
but lacks the characteristic struc tures of the organic version.
As with other gems and ornr:mental materials of organic origin,
the term synthetic is nc very meaningful.
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