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[Roger Warin]

Hello, about tanzanite pleochroism

I enjoyed doing this little manipulation (“manip”), as they say in chemistry.
On my last visit to the Mineralientage (Munich), I didn’t only see Masterpieces.
I bought a tiny specimen of strictly colorless zoisite for €100, with a Tanzanite label.
It is becoming difficult to find an unheated specimen.
The specimen was purchased from a stand selling stones for cutting.
In gemology, these unheated crystals regain a high value compared to the “sapphire” tanzanites that have been so numerous since the end of the 1980s.
Is my crystal a zoisite or its tanzanite variety, since it would have turned blue after heating? At €100 per gram, we can hope so.
I examined the trichroism of this zoisite, with some success, I think.
What do you think?

First, I took 2 shots in natural light with a digital camera, from the front (or back side) and from the side.

With the microscope, it is impossible for me not to see the trichroism with lateral spots.

Then I put the crystal under the binocular:
1) With side spots.
2) Lower lighting like a thin section:
polarized or unanalyzed light.

With cross polarization, hues are enhanced.
Why ?

Crystal dimensions : weight = 1.0 g
base of the monoclinic prism ≈ 5 mm.
height ≈ 12 mm.