I would place a bet that it has either been heated,
irradiated, or diffusion treated. Take a look at the corner meets
with a microscope and see if the color is inconsistant.
Unfortunately, I don't have a microscope, but maybe I
could borrow one. Could you explain what you mean a little more?
Where am I looking, and for what?
Noel, perhaps the best way to do this is to first find a shallow
glass dish or, better yet, a shallow, white plastic (or Tupperware)
dish that will fit on the stage of the microscope. Basically, you'll
be using it as an immersion cell similar to the one found at this
You must diffuse the light from the base of the microscope, so use
white plastic, or place a sheet of white paper under the clear glass
You probably don't have methylene iodide to immerse your stone into,
but water will work well enough. Baby oil will work better as it's
refractive index is closer to that of topaz. Put the stone in the
immersion cell, cover it with the liquid of your choice and place it
under the microscope. Hopefully, you'll be able to see through most
of the stone even though it is mounted (I believe you did say you
had mounted it as a jewelry piece).
If it has been diffusion treated (I'm not sure anyone has ever
diffusion treated topaz, but that is what was suggested), you'll see
the color of the stone has concentrated along the facet junctions.
Or possibly around the rim of the outline of the stone, or mainly
the center of it. Typically, untreated stones will be uniform in
their depth of color under immersion, while diffusion treated stones
tend to have their color concentrated in the center or along facet
junctions when viewed under immersion.
James in SoFl