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Tanzanite (blue zoisite)
The basically blue variety of zolsite discovered
in Tanzar in 1967 is commonly known as tanzanite.
Appearance This gem has a characteristic
blue colusually with a violet tinge. In lighter-colored specimens,almost
lavender. This is the principal color, visible from table
facet in cut stones, because another characteristic tanzanite
is strong pleochroism from violet-blue to viol, grayish, or
greenish. It has vitreous luster. The stones ha. few inclusions,
where present, these sometimes look
thin, parallel tubules. It is normally given a round or ov
mixed cut, but the step cut is also used.
Distinctive features The particular
color, combined with the type of pleochroism described and
moderate lust - make it fairly easy to distinguish. It can
sometimes reseble cordierite, but this has much lower refractive
indic and lower density. It is sometimes confused with sapphibut
compared with this, it is visibly less lustrous and mL less
hard. It also has different pleochroism and differ, refractive
indices. It is said to have very low resistance ultrasound.
Tanzanite jewelry should, therefore, never : cleaned with
the ultrasonic cleaners commonly used by jewelers and watchmakers.
On a number of occasior stones thus treated have suffered
irreparable damage.
Occurrence Very limited quantities
are found, almost e clusively in Tanzania, where, moreover,
the chief depos - apparently nearly exhausted.
Value Given its attractive
color, its rarity, and the pur ity which greeted its discovery,
the value of tanzani, quite high, little less than that of
the violet-blue sapphir, resembles. But it is rarely seen
on the market and is much a collector's item. Its modest hardness
makes suitable for rings which are, of course, susceptible
tc knocks and abrasion.
Simulants and synthetics Being
little known and of very recent history, this stone has neither
been imitated not produced synthetically.
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