The World's largest blue topaz is called the , "Siam Akara Manee", (giant gemstone of Siam), it weighed 30,000 carats in rough form when it was discovered in Namibia.
Not to totally dispute this,as anything is possible.But I traveled
this planet chasing down all the Topaz I could buy during the boom.
Never heard of any Topaz coming from Namibia,and word of large ones
would have gotten around the market for sure.There is only two
locations that I am aware of that can produce giant size
Topaz,Marambia area in Minas Gerias,Brazil and the Ukaraine,former
Russia which produces natural(irradiated in nature anyway) Brown
crystals.I have handled crystals from there up to 15 kilo(75,000cts)
and from Marambia the largest I worked on was 35kg.I have read some
mention of a new find of large Topaz crystals in Vietnam. The largest
crystal I ever heard of was discovered in Trace Barros,Minas
Gerias,Brazil.It was like 30 meters and they could not get it out in
one piece,so broke it up “in situ” to remove the spots of gem
material. Most large deposits of White Topaz in the world run 150gm
size as the larger
crystals.Nigeria,China,Mt.Surprise,Australia,Rondonia mine
Brazil,Texas,USA.Small brown ones are found in Mexico,Utah,USA.At
Mimosa do Sul,Espirato Santo,Brazil you can find up to 1-2 kilo
size.Point of interest,to treat over 20-30gm to Blue is impossible in
Linier Accelerator or Nuclear treatments.The static electricity would
shatter them.You can lay them in a Colbolt 60 walk in room and give
them Gamma dosage.Typicly .5 megarad per hour.To achieve a decent Blue
you need at least 500 megarads,so it can take months.Then you have the
most difficult task of trying to heat such a large piece,the second
step in treatments,without breaking the stone. Mark Liccini