AboveThis gem shows how the colour varies between blue and violet.  The golden gleam in one facet is a reflection from the gold mount. Inclusions like this are quite rare in tanzanite.  They are probably growth tubes, and would have contained liquid as the gemstone formed.
Looking at the picture the inclusions are very noticeable.  In reality they're almost invisible, I had to arrange the lighting to highlight them.

Click here for a larger image

Below: Detail of the inclusions, the best I could achieve with our equipment.  The broad rough line near the top is an edge between facets on the back of the stone, rather out of focus.  The other horizontal and parallel lines are the tube-like inclusions.  This stone showed some damage by chipping to facets at the back, not visible to the naked eye.

Tanzanite

A splendid clear stone.  It is mainly blue, but parts of the stone will also look violet, it depends on the angle of the light hitting the crystal.

Treatments before purchase

Almost all tanzanite is heat-treated, when first mined it's a muddy brown colour.  The treatment is permanent.
Only a few pieces need no treatment, these are even more attractive if you are ever lucky enough to see one (I never have).
Inclusions and fractures are rare, so fracture filling is very unlikely.  However we have seen reports that some colour enhanced stones are appearing.  As yet there is insufficient information to give any further guidance.
It's not a treatment, but you must be aware that some stores are selling tanzanite coloured CZ, so read descriptions carefully.  If the stone's name is not spelt exactly as shown here, it's almost certain to be a trademark for blue CZ.

Caring for Tanzanite

The stones are comparatively soft, and will be scratched by household dust.  Do not wear when doing manual work (including housework).
They can be soaked in lukewarm water to clean them, but should not be soaked in Silver Dip.
Treat with care, and enjoy these beautiful stones for many years.  They look splendid, especially when seen with diamonds, and are ideal for special occasions.