Chatoyant beryl (a.k.a. cat’s-eye aquamarine when it is blue-green
in colour) is not particularly well-known, but it is quite
sought-after as a collector’s item. In addition, because the name
"aquamarine" has such good name recognition, I would think that it
might well appeal to the discerning ordinary consumer as well as the
collector. It can be very attractive, although the cat’s-eye effect
isn’t as fine as in chrysoberyl.
Also, would anyone know whether heat will make this bluer and
what the specs are for heating?
I've never actually heat-treated any myself, but I've read a little
about the heat-treatment of ordinary aquamarine. Heating blue-green
beryls usually results in the green tones fading, leaving the blue
behind. I believe that the required temperature range starts at
about 650 degrees centigrade, although I know that hotter
temperatures are also used. N.B. if you overheat beryl it will
eventually decompose into a type of glass, becoming opaque and
unattractive in the process.
However, there is a general principle in gemstone treatment that
says that it is advisable to only heat-treat the cleaner, more
flawless stones. If you heat-treat a stone with many inclusions, you
are more likely to end up with breakages. Chatoyancy in beryl is
normally due to many inclusions: fine, parallel growth tubes that run
along the c-axis of the crystal. These growth tubes might lead to an
increased risk of the stone fracturing when you heat it. However, I
do know that beryl has a pretty low coefficient of thermal expansion,
so in theory this might mean that the risk of fracturing is slightly
lower than for some other gemstones (particularly at the
comparatively low temperatures required for beryl). If you do
decide to heat-treat it, you might want to ensure that the
temperature rise is slow and gradual, and that the stone is not
cooled down too quickly afterwards. But you should probably consult
an expert on gem heating first!
The stone sounds interesting - may I ask where you got it?