Creation or Treatment Method: Imitations only, no synthetic tanzanite
Identification Tools Required: Magnification, Chelsea filter, calcite dichroscope, refractometer.
How to Identify:
Primary Tests: There are two very important factors to remember when it comes to tanzanite.... #1 is that there are no synthetic tanzanites, only imitations. #2 is that all tanzanite imitations can be identified using only the Chelsea filter and dichroscope. Here is a list of the known imitations and how to identify them:
Tanzanite will be known for two very distinct reactions to the Chelsea filter and dichroscope. If you study these and remember the results you will have no problem identifying the imitations:
Chelsea Filter: Light golden red to light brownish red
Synthetic Forsterite: This is the best known since it is a double refractive gemstone of blue color and in the same relative refractive index range of tanzanite. But here are the reactions:
Chelsea filter: Inert
Synthetic Corundum: Easily separated by refractive index but even more easily using the Chelsea filter and dichroscope.
Chelsea filter: Inert
Dichroscope: Blue/Greenish Blue
YAG: This stone offers no blue/purple color as natural tanzanite, but once again no need to get to carried away with testing.
Chelsea filter: Strong Red (too strong for natural)
Polysilicate: This material is essentially glass and has a variable RI that is usually in the 1.58 range. But since it is a composite stone with a blue interior and purple exterior layer, the blue/purple colors of this material to the untrained eye can be a very good emulator of tanzanite. And here is the key on this, this material has been doped to have a red reaction to the Chelsea filter. So for the untrained gemologist who just sees the blue/purple color and throws a Chelsea filter on the stone the reaction may be confusing. But by also using the dichroscope the true nature of the stone can be seen
Chelsea filter: STRONG red
Secondary Tests: Refractive index will be a secondary test if the Chelsea filter and dichroscope are not available. Beyond that no further tests should be required.
Repair and Setting: All of the gemstones used to imitate tanzanite are fairly durable. No direct torch or heating by torch. Recommend to remove or heat sink before any repairs are started. In general these are fairly hard stones that will withstand normal wear and tear of the work bench.