Color change garnet!
a more romantic name and one that is in a real sense more accurate
might be Alexandrite Garnet. This is the first and only known example
of blue garnet. For the past fifty years, the statement “garnet
comes in every color but blue” would be completely accurate.
The other uncanny thing about this garnet is that it changes color
exactly like an Alexandrite.
I saw one for the very first time in 1990 during
a trip to East Africa. The gem weighed one half carat and looked
exactly like an alexandrite from the Hematita strike in Brazil.
Others have compared the Madagascar color-change to Russian Uralian
Alexandrite as well1. The price was
high but as it turned out I didn’t see another for almost
eight years and the next one was not nearly so fine.
The stone is a pyrope-spessartine garnet. This
would give the stone a high rating for durability. Both pyrope and
spessartite garnets have hardness’s between 7-7.5. In practice
this usually means 7.25, which would be very resistant to scratching.
High concentrations of Vanadium with a bit of added chromium appear
to be responsible for the color shift.
Like alexandrite, the Madagascar gem is a night
stone. A lady of the evening who puts her best foot forward beneath
the light of a flame. The primary hue under incandescent is a beautiful
deep grapey purple. Sometimes a tiny bit of red can be seen flashing
from the depths of the gem. In finer stones, the afternoon daylight
hue is green-gray-blue to blue. A limpid crystalline stone is always
beautiful and thus desirable.
Beating Alexandrite at its own game:
The color change of this gem is truly remarkable.
Alexandrite is a doubly refractive stone, each ray that enters the
gem crystal divides into two rays each containing half the rainbow.
Alexandrite has, as it were, a good excuse to change color. Alexandrite
garnet is singly refractive and has no such excuse.
The stone is extraordinarily rare. The rarity
increases dramatically above one carat. In my experience most stones
over the carat become murky and gray. A fine one-carat would be
a find indeed.
1_Schmetzer & Bernhardt, Garnets
from Madagascar with a Color Change from Blue-Green to Purple.,
Gems & Gemology, The Gemological Institute of America,
Vol. 35, #4., Pg.199