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Brightly Fluorescent Hyalite Opal from the Erongo Mountains, Namibia

This brilliantly fluorescent specimen from the Erongo Mountains of Namibia features colorless to greenish-yellow, transparent, glassy bubbles of hyalite opal (Opal-AN) covering a granite matrix. The hyalite opal shows a bright green fluorescent response under all UV wavelengths, and also exhibits yellow/green daylight fluorescence under sunlight. The green fluorescent response seen in this material is due to trace amounts of uranium included in the opal silica. Due to the uranium content, this specimen is moderately radioactive and was measured at 800 cpm at 1 cm. The size of this piece is 14.3 x 9.5 x 3.2 cm, and it weighs 360 grams.

As shown in the photograph above, the hyalite responds with brilliant green fluorescence under short wave UV (254 nm).

Bright green fluorescence is also seen under long wave UV (365 nm), but is less bright than that seen under short wave UV.

Same specimen shown under visible light (illuminated by LEDs).

When viewed outdoors under indirect sunlight, the hyalite shows green-yellow daylight fluorescence. The above photograph was taken mid-day under an overcast sky.


This close-up image shows the individual botryoids of the hyalite under visible light. FOV = 20 mm.


The macro images above show the fluorescence of the individual botryoids under short wave UV (left) and long wave UV (right). FOV = 20 mm. Click on the images for a larger view.

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