Topaz and Feldspar from the Zapot Pegmatite, Nevada
Contributed by: Michael Crawford
minID: T2K-EYJ
Date: Jul 9th, 2025
Locality: Zapot Pegmatite, Gillis Range, Fitting Mining District, Mineral County, Nevada, USA (See on Mindat)
Size: 13 x 15 cm
Description:
This specimen has several topaz (Al2(SiO4)(F,OH)2) crystals in a feldspar matrix. The specimen comes from Zapot Pegmatite, Zapot Pegmatite. The topaz fluoresces brightly under longwave UV illumination, is dim in midwave and shortwave UV illumination. The topaz crystals have different yellow hues and brightness of longwave fluorescence. The longwave emission spectrum of the brightest crystal has a broad peak with a maximum at 561 nm. The LW spectrum of the darker yellow crystals has two peaks, one at 428 nm and another around 550 nm. There are a couple of areas on the topaz that fluoresce a bright yellow in shortwave UV light. The peak of the emission spectrum of the shortwave yellow is shifted to 532 nm. There are no references that describe the activator(s) for this yellow fluorescence and the change in hue at different illumination wavelengths.
Shortwave fluorescence reveals three types of feldspar in the specimen. A lot of amazonite is exposed on the backside of the specimen and there are many small patches of light blue amazonite present in the white light image. Under shortwave UV illumination the amazonite appears to be non-fluorescent, but there are areas of red fluorescence from feldspar. The feldspar has bright blue-white fluorescence under longwave UV illuminations. Longwave and shortwave emission spectra of this blue-white fluorescence have peaks around 440 nm to 450 nm. The shortwave emission spectra reveal there are two types of red fluorescent feldspar. Microcline feldspar has an emission peak at 688 nm and albite has a broad peak with a maximum in the near infrared at 724 nm. The spectrum indicates the sodium feldspar albite.
The image of near infrared fluorescence differentiates these two feldspars. The albite is much brighter in the 730 nm bandpass image. The color infrared image is composed of the 730 nm near infrared image assigned to red, the red visible band assigned to green, and the green visible band assigned to blue. This image shows the amazonite in red, the albite in white and orange, and the microcline as yellowish green.
Summary of luminescence responses:
Topaz (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Shortwave (255nm LED) UV light: Yellow
- Fluorescence under Longwave (365nm LED) UV light: Blue
- Fluorescence under Shortwave (255nm LED) UV light: Red
- Fluorescence under Shortwave (255nm LED) UV light: Red