Database of luminescent Minerals

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SCHEELITE

Chemical Formula: CaWO4

Familly: Tungstates, Molybdates

Status: IMA-GP

Crystal System: Tetragonal

Mineral for Display: Yes

Associated names (luminescent varieties, discredited names, synonymes etc.):  cuproscheelite,  molybdoscheelite, 

Luminescence:

UV Type Main color Intensity Observation Frequency
Long Waves (365nm):      Violet Pink Very weak
Mid waves (320 nm):      Red Medium
Short Waves (254 nm):      Bluish White Very StrongAlways
Other colors LW:                    
White , Orangy yellow , Orange , Violet red ,
Other colors MW:               
Orange Red , Red , Violet red ,
Other colors SW:                              
White , Yellowish White , Pinkish White , Pale Yellow , Tawn , Yellowish ,

Daylight Picture


SCHEELITE, China
Photo and Copyright: James Hamblen
Site of the author
Used with permission of the author

Short Waves Pictures (254nm)


SCHEELITE under UVSW
Photo and Copyright: James Hamblen
Site of the author
Used with permission of the author

 

Galerie de photos:

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     To the gallery (8 images in the gallery)

Phosphorescence (in the common meaning of the term) seen by naked eye:

No Data

Thermoluminescence: Yes

Comments:

A very thin  coating of SCHEELITE on WOLFRAMITE makes it glow and give the impression that this mineral is luminescent.

The tungstates of calcium, strontium, magnesium and zinc, and the molybdates of calcium are known to show luminescence upon excitation by cathode rays or short-wave ultra-violet radiation. It is commonly assumed that this luminescence is characteristic of the tungstate and molybdate groups. The reason why other tungstates and molybdates are found to be non-luminescent is probably the temperature-quenching (see Nature article by F.  A. Kröger in 1947 in the bibliography).

Main Activator(s) and spectrum:

Most Common Activator: WO42-

Other activators:            Sm3+ , Eu3+ , Dy3+ , Ho3+ , Er3+ , Tb3+ , Pr3+ , Nd3+ , Yb3+ , Tm3+ ,

Peaks in the spectrum (nm):

WO42-: Broad band centered at 425 - 435nm  (Lifetime: 9μs @ 405nm)
Tb3+: 439nm
Dy3+: 488, 575nm
Sm3+: 609, 647nm
Pr3+: 607nm


Spectrum: Michael Gaft, Petah Tikva, Israel. Plot: Institute of Mineralogy, University of Vienna, Austria, with permission of the authors.

            ...

  To the spectrum gallery (9 spectra in the gallery)

Comments on activators and spectra:

Scheelite is characterized by broad luminescent bands centered at 425 - 435 nm (blue emission) of intrinsic activator (WO4)2- groups and impurity (MoO4)2- groups.

 Those broad bands are attributed to an intrinsic slight distortion of the [WO4]/ [MoO4] tetrahedral group. [WO4] lifetime: 9μs (@ 405nm).

Such strong bands prevent in many cases the detection of lines of rare-earth elements, especially Tm, Er and Ho, which have weak luminescence in the corresponding spectral range.

Yet, scheelite incorporates often tens to thousands of ppm RRE in substitution for Ca giving sometimes typical peaks in the fluorescence spectrum. Visible peaks in relation with the presence of REE: 488 et 575 (Dy3+), 609 et 647 (Sm3+), 439 (Tb3+) et 607 (Pr3+). But the lines of certain REE may be hidden by stronger luminescence of others REE. For example, the luminescence of Pr3+ is difficult to detect because its radiative transitions are hidden by the lines of Sm3+, Dy3+ and Nd3+, the luminescence of Tm3+ is concealed by Tb3+ and so on.

The pegmatitic and hydrothermel scheelite  shows the lines of Erbium and Terbium, while scheelite occurrences related to eruptive complex and sulfide ore shows dominantly the lines of the REE of the Cerium group.

Under cw laser excitation at 532 several narrow lines have been found in red and IR part of the spectrum connected with Nd3+ and possibly Sm3+ centers.

Green emission due to (MoO4)2-(Tarashchan) or possibly Pb (Blasse).

 

The color of the fluorescence of scheelite gives an idea of the unwilled presence of molybdenium in the ore. Concentrate of scheelite not penalized for molybdenium have a distinct blue fluorescence color. Those that fluoresce white are borderline  and contain roughly 0,35% to 1% of Mo. And scheelite that fluoresces distinctly yellow contains more than 1% corresponding to a transition to powellite. Higher than 4,8%, the yellow fluorescence color stays unchanged and cannot anymore be used as an indication of the percentage of Mo. Using this property, a method was  developped by R.S. Canon jr. (1942) while studying tungsten deposits in the seven Devils mining district of Idaho. A serie of finely powdered synthetic preparation or natural ore of known composition are permanently mounted in circular areas on a black card, being placed in order of increasing molybdenium content. There are twelve standard values on the card: 0,05, 0,19, 0,33, 0,48, 0,72, 0,96, 1,4, 2,4, 3,4, and 4,8% plus a pure calcium molybdate (48% Mo). Alternating with the covered circle are circular holes of the same size. The card is used by placing a hole over a powdered sample of the scheelite ore to be tested and comparing the fluorescence color of the sample with those of the adjacent standards. The sample will be found to have a fluorescence color according or between two standards and hence the approximate composition could be defined.

 

Best Locality for luminescence(*):

(*)Data are not exhaustive and are limited to the most important localities for fluorescence

Bibliographical Reference for luminescence:

Luminescence Reference on internet:

Mineralogical Reference on internet:

  http://www.mindat.org/show.php?name=Scheelite

  http://webmineral.com/data/Scheelite.shtml

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