Scheelite and Calcite from the Huanggang Mine, Chifeng, Inner Mongolia, China
Contributed by: Michael Crawford
Date: Jul 26th, 2025
Locality: Huanggang Fe-Sn deposit, Hexigten Banner (Keshiketeng Co.), Chifeng City (Ulanhad League; Chifeng Prefecture), Inner Mongolia, China (See on Mindat)
Size: 6.5 x 11.5 cm
Description:
A scheelite and calcite specimen from the Huanggang Mine, Chifeng, Inner Mongolia, China. The scheelite crystal fluoresces white under shortwave illumination. The crystal likely contains a small amount of molybdenum that shifts the fluorescent color to a longer wavelength. This shift is shown by the spectra in the fifth image. “Pure” scheelite is bluish white under shortwave illumination and the shortwave emission spectrum has a maximum at 428 nm. The shortwave emission spectrum of this scheelite crystal has a maximum at 447 nm and the width of the fluorescent peak is much broader than the “pure” scheelite spectrum. The spectrum also extends into green and red wavelengths. The white color of the scheelite shortwave fluorescence results from the broader range of wavelengths emitted by this crystal.
The shift in the color of scheelite shortwave fluorescence due to molybdenum replacement of tungsten in scheelite has been known for more than 80 years. Scheelite (Ca(WO4)) – powellite (Ca(MoO4)) form a solid solution series where tungsten and molybdenum are readily interchangeable in the crystal structure. A patent for a color chart that relates the scheelite fluorescent color to the percentage of molybdenum replacement was granted to R.S. Cannon in 1944. Cannon determined that SW scheelite fluorescence changed from bluish-white when pure to white at 1.5 molar weight percent molybdenum, and it became yellow at 10 molar weight percent molybdenum. Adding more molybdenum kept the fluorescent color the same as pure powellite (yellow).
This scheelite crystal is non-fluorescent under longwave UV illumination and is yellow under midwave UV illumination. The midwave emission peak is at 505 nm. The yellow midwave is likely caused by the molybdenum replacement of tungsten.
Calcite fluoresces orange red under all UV wavelengths. The emission spectrum has a peak at 611 nm. Calcite fluorescence is activated by manganese replacing calcium.
Summary of luminescence responses:
Scheelite (Mindat) (RRUFF)
- Fluorescence under Shortwave (255nm LED) UV light: White
- Fluorescence under Midwave (305nm LED) UV light: Yellow
- Fluorescence under Longwave (365nm LED) UV light: Red
- Fluorescence under Midwave (305nm LED) UV light: Red
- Fluorescence under Shortwave (255nm LED) UV light: Red