Gemmology Question Heat treatment

[treasurehunter]

If a stone has rutile needles intact but also some evidence of heating does the evidence of no Heat overrule the evidence of Heating or is it vice a versa?
Gemmologist Please Respond

 

[athenaworth]

Rutile needles can stay in tact with light heating.

 

[treasurehunter]

How does one tell if the heating was natural process IE underground or an unnatural process?

 

[chrono]

Signs that tell you the corundum is unheated (or even if heated naturally, as long as these are present, one can consider this unheated because the natural heating temperature was low enough to leave these intact).

 

[chrono]

You can see that the inclusions have fused, healed or "exploded" after being heated.

 

[chrono]

A more thorough paper by SSEF, complete with pictures.
http://www.ssef.ch/fileadmin/Documents/PDF/650_Presentations/HK2010March_PinkSapphire.pdf

 

[GemAgents1]

If there is indication of heat the needles are meaningless. Most tanzanite is heated and many of them have needles.

 

[treasurehunter]

Thank you Chrono,SSEF states Intact Rutile needles is not a indication of No heat.
I guess I base heat/no heat just on the crystals then ? or would one need Spectroscopy to be sure if its heated or not?

 

[chrono]

Thank you Chrono, SSEF states Intact Rutile needles is not a indication of No heat.
I guess I base heat/no heat just on the crystals then ? or would one need Spectroscopy to be sure if its heated or not?

Correct, because when heated at low temperatures, some rutile needles may remain intact, so it is best to study the other inclusions for signs of heat/no heat. If there are no crystals, then you will need better equipment to make that call.