A strange parcel of crystals from deep in the Oromia state, Southern Ethiopia, came to the office last week. The crystals richly green, had a blue-green color and olive’s color another way.

We noticed that several crystals looked reddish with a light when viewed in particular directions. The phenomena appears to be an unusual and not-entirely-explicable interplay between pleochroism, flourescence and also the usambara effect.

Chrome Tourmaline
Chrome Tourmaline from Southern Ethiopia’s Oromia Region

 

Partial Usumbara Effect ? Or not. Limited Red Fluorescence in Chrome Tourmaline.
Partial Usumbara Effect ? Reversed Usambara? Or not? Limited Red Fluorescence in Chrome Tourmaline that only runs a little way in the crystal.

 

Red Flourescence Or Usambara Effect ?
Red Flourescence Or Usambara Effect ? Full-length red color that is only visible down the C-Axis. What exactly this phenomena is debatable but is probably an interplay between pleochroism, flourescence and the usambara effect.

 

Fluorescence Through a Chelsea Filter
Fluorescence Through a Chelsea Filter due to High Levels of Chromium.

1 Comment

  • Asbjørn Halvorsen
    Posted October 4, 2019 8:07 am 0Likes

    Hi,
    You show some interesting photographs, with the question Usambara effect, or not? Photographs 2 and 3 show clearly what I described as “visible light fluorescence” in a paper on Usambara effect in The Journal of Gemmology, January / April, 2006. The same phenomenon can be observed in a chlorophyl solution. My understanding is that Usambara effect and “visible light fluorescence” in a way is related. The causes are not the same, but the effects seem to be related. Maybe also the “absorption modified dispersion (AMD”.

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