Ulexite fluorescence

Ulexite: (NaCaB5O6(OH)6•5(H2O)) (hydrated sodium calcium borate hydroxide) is commonly known as "TV Rock" due to its ability to transmit light along the closely packed parallel fibres from which the mineral is composed.

The images are in white light (bottom) and 384nm LED light (top). The fluorescence spectrum is excited with a 365nm LED. The pink rectangle at the bottom tight of the spectrum shows a small second-order (grating) leakage of the LED lamp which appears at twice the emitted wavelength. Otherwise, the fluorescence spectrum is almost perfectly smooth except, perhaps, for a very small feature at 460-470nm: is this a calibration error or does it represent some physics?

For a comprehensive discussion of the fluorescence spectra of the most important borate minerals, see the article by Axel Emmermann in Volume 34 (2011) of the Journal of the Fluorescent Mineral Society.

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