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Red Fe3+ fluorescence in alkali-feldspar

Trivalent iron gives a red fluorescence in feldspars. It can even be used to distinguish between sodium and potassium feldspar. The emission maximum shifts to the red with increasing Na content. Top view, an albite (Na-feldspar) from Konso, Ethiopia. Bottom view, a potassium feldspar (microcline) from Teller Co, Colorado, USA. Both exhibit the typical green "amazonite" (not an official mineral name) colour caused by a combination of lead, crystal water and radiation. The emission spectrum shows the maximum for both samples. Photo's with a 255 nm LED, spectra with a 275 nm LED (it gives no false emissions from the LED surroundings)

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