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Diamond
Imitations and Others
The appearance of rutile on the market started a hunt
for crystals that, when cut, would resemble diamonds.
A problem exists with rutile because of its inevitable
yellowish color. This problem was solved with the introduction
of strontium titanate in 1955. Closely related to rutile,
strontium titanate's advantage is its pure white color,
with no yellowishtinge. The hardness is, however, 6
on the Mohs scale, still too soft to be very useful
in rings. Another advantage of strontium titanate is
its dispersion, which, though very high (four times
higher than diamond), is lower than that of rutile and
thus more realistic.
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Cut
gems do resemble diamonds very strongly, especially
when they acquire a slight oily film which further cuts
down the dispersion. Strontium titanate does not exist
as a natural mineral. Its softness left an opportunity
for a still better diamond imitation material. |
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This
marketing gap was filled by a material called YAG, an acronym
for Yttrium Aluminum Garnet. YAG is one of a family of so-called
"gar¬nets," named because their internal atomic
structure is like that of the natural garnets. But here the
similarity ends, because YAG and its brothers with similar
rare-earth chemistries, such as GGG (Gadolinium Gallium Garnet),
do not occur in nature.
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DIAMONDS,
GEMSTONES & CRYSTALS
FACTS & FIGURES |
| YAG
was originally grown for use in lasers, which
is still its major application. It was accidentally
discovered that, when properly cut, YAG strongly
resembles cut diamond, even though its dispersion
is relatively low. In addition, the hardness of
YAG is about 8 on the Mohs scale, so cut gems
are durable and do not scratch easily.
YAG
can be colored richly by impurities, and cut stones
may resem¬ble emerald, kunzite, sapphire,
and other gems, although YAG's are too brilliant
and hard to be convincing substitutes for most
gems.
. 
The
newest and most important imitation diamond material
is cubic zirconium oxide, or "zirconia."
This material is as hard as YAG (8.5), hut has
a much higher dispersion. In fact, the dispersion
of zirconia is slightly higher than that of diamond,
giving extremely realistic "fire" to
cut gems. Such stones are lively, hard and durable,
and virtually indistinguishable from diamond to
the untrained eye. Small zirconia gems in jewelry
settings will undoubtedly pose severe detection
problems for the jewelry trade. Zirconia sells
for several tens of dollars per carat, offering
the consumer a stone with much of the beauty of
diamond at a fraction of the diamond price. |
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Other
gem materials created solely in the laboratory include lithium
niobate, sometimes sold as "Linobate," with a Mohs
hardness of 6, yttrium aluminate, and potassium tantalite
- niobate, whose chemical acronym is KTN.
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