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GGG
Having very similar characteristics to diamond,
in some respects more so than YAG, GGG partially replaced
the latter as a diamond substitute in the 1970s, despite its
much higher cost. But it has in turn been superseded by cubic
zirconia, which has still better characteristics and is a
lot cheaper.
Appearance Transparent and colorless (or
with a yellow-brown tinge), it is seen almost exclusively
in the form of brilliants. It bears a strong resemblance to
diamond, but since the stone is not very hard, the facet edges
often have i
small chips on them.
Distinctive features The refractive index
is higher than that of YAG, a similar, more widely distributed
product, but still less than that of diamond. Here, too, the
effects on total internal reflection are such that if a stone
is tilted gradually, a dark, transparent area is visible from
the table facet, corresponding to certain pavilion facets,
which let the light through instead of reflecting it. The
girdle is usually different from that of diamond; less clearly
cylindrical and with a striated appearance, as if it had been
smoothed with a file. Its density is so high that, in the
case of a loose stone 8 to 10 millimeters in diameter, it
can be appreciated simply by weighing it in the hand.
Cost Higher than that of modern synthetic
stones, but less than most costly synthetics like emeralds.
It is hardly ever seen on the market nowadays.
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