Dear Gerry,
I know you mean well and I really do not want to get into another
debate with you, but here I go.
I go to Mexico all the time, grew up there still have a house there,
run my biz there and I guaranty there is no known citrine deposit
there of commercial value. (madeira citrine or any citrine deposit
for that matter) Somebody is giving you bad info. Madeira is from
Brazil.
All the topaz in Mexico is from San Luis Potosi area inspite of the
label “Guerrero” (Guillero sic) that was given to it years ago.
This material does turn darker with cobalt irradiation but is not
light stable before or after this simple irradiation procedure. I
heard it is stable if treated to blue but I am not sure of this.
This irradiated Mexican material looks nothing at all like Ouro
Preto Imperial Topaz - Not in the rough or in the finished gem. The
color of all irradiate topaz whether in the brown or in the blues is
nothing like fine Imperial from Brazil. Brazilian imperial can be
fuchsia colored in its finest natural colors. BTW inspite of what
others have said here there is a difference in topaz both chemically
and crystalographically (whew) between Ouro Preto Brazilian
imperials and other worldwide topaz sources. I have gone over this
in past posts. Just look at the crystal morphology and color range
to see how different it is.
It is not just heat treatment that is necessary after irradiation to
turn topaz to blue, but also you need topaz that will turn (not all
will) and you need the correct type/intensity of radiation. Cobalt
60 is not used for blues, but Linacs and other irradiation sources
are.
And as far as not being able to trust dealers… stop generalizing
!
Thanks and I am not trying to make you mad, just clear the air a
little. I have tons more to say on this thread. I have seen alot of
partial truths about the topaz and citrine subject lately. Being the
end of summer, I have just been a little too distracted to get
involved till now.
Respectfully,
Steve Green Rough and Ready Gems www.briolettes.com