are nothing short of incredible, as you learn what they are and how
they got to be inside the gem. One of the easiest categories of inclusions
to identify are fractures. Emeralds almost always have internal fractures,
while they are uncommon in most gems. Tiny, internal fractures that
don't reach the surface will have minimal effect on the durability
of the gem. The fact that they have gone through the cutting process
without damage attests to that. Larger fractures, or those close to
a thin edge, are significant.
If a fracture
reaches the surface of the gem, it has the ability to absorb liquids.
Over time this can absorb dirt and skin oils, loosing some of its
this feature is used to absorb oil or other substances with the same
RI as the gem. This makes them much less visible. To see them, you
need to look very closely and get the light on them from just the
right angle. If you see a multicolored radiance, like an oil slick,
you have spotted a filled fracture.
have at least a slight bit of curvature in them. Look carefully to
see this. If you encounter one that is perfectly straight, that is
most likely a cleavage fracture. Gems have cleavage planes that are
much like the grain of wood. Along the cleavage plane the gem splits
easily. Finding a cleavage fracture in a gem is a sign of significant
most common type of inclusion are other minerals. These can be small
bits of debris or miniature, whole crystals. Afghani peridot sometimes
has clusters of tourmaline that look like flies. Spinel can be included
with tiny spinel crystals arranged in a plane. These are often spectacular!
are transparent. How visible they are depends on their RI. If they
are significantly different than the surrounding crystal, they will
jump right out at you. In other cases, like spinel in spinel, they
are nearly invisible. To see them you need to have a dark background
behind the gem and light coming in from the sides.
is found in several gems but it is particularly common in corundum,
spinel and garnet. This is a pattern of very slender, thread like,
crystals. When they are fine enough and all arranged in the same direction,
you get the impression that you are looking at the gem through a fine
layer of silk, or seeing it inside the gem. The greater saturation
of the silk, the more brilliance of the gem will suffer.
be surprised to see what looks like a fingerprint in a gem. That is
called a "healing fracture." At some point in the crystal's
history, it got broken. Then the conditions for growth became present
and it grew back together, or healed.