Database of luminescent minerals 

GROSSULAR   (French name: GROSSULAIRE )

Chemical formula: Ca₃Al₂(SiO₄)₃

Family: Silicates

Status: IMA-GP

Crystal system : Isometric

Display mineral: NON

Associated names (luminescent varieties, discredited names, synonyms, etc.): grenat,  hessonite,  hydrogrossulaire,  tsavorite, 

Luminescence:

Daylight picture

GROSSULAIRE Lake Jaco, Chihuahua Mexico;
Col. G.Barmarin; Photo: G. Barmarin

Longwave (365nm) picture

GROSSULAIRE Lake Jaco, Chihuahua Mexico;   UVLW
Col. G.Barmarin; Photo: G. Barmarin

Shortwave (254nm) picture

GROSSULAIRE Lake Jaco, Chihuahua Mexico;   UVSW
Col. G.Barmarin; Photo: G. Barmarin

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Phosphorescence (in the common sense of the term) observable with the naked eye:

No phosphorescence visible to the naked eye under any type of UV

Thermoluminescence: OUI

Comments:

Grossular garnet from Lake Jaco, Chihuahua Mexico, may be found as dark cherry red crystals, with vesuvianite.

Under either MW or a filtered high pressure UV source, these garnets fluoresce brilliantly in a pure red.

Mont-Saint-Hilaire: grossular OH-bearing (hibschite)

Activator(s) and spectrum:

Activator(s): Cr³⁺, Mn⁴⁺,  Mn²⁺ ,  V²⁺,  

Peaks in the spectrum (nm):

Broad band peaking at 611nm, peak at 489nm and 713nm (échantillon en collection)

Cr³⁺ : Lines at 690, 694, 698 and 707nm

Mn²⁺ substituting to Ca²⁺ : band around 590 -605 nm

Mn³⁺ : broad band at 653nm

Mn⁴⁺ : broad band at 670nm

V²⁺ : peak at 717 nm  (Gaft)

Col. G.Barmarin; Photo: G. Barmarin

Spectrum Galery:

  
  Go to the galery (2 spectra)

Comments on spectrum and activators:

The color is identical to that of red-fluorescing ruby corundum or spinel. As with those minerals, chromium in place of aluminum is the likely activator. Other activator: V²⁺ (717 nm), Nd³⁺ (462, 476, 482,501 nm) and possibly Mn²⁺ band around 605-610 nm (decay time: several ms).

Natural grossular luminescence was studied by continuous wave (CW) luminescence technique and has been connected with Cr³⁺ centers, which substitutes for Al³⁺ and occupies a site with distorted octahedral symmetry (which in fact is trigonal C3i). Trivalent chromium in grossular occupies high crystal field position.

The luminescence spectra of Cr3+ in grossular at room temperature contain a strong broad band peaking at 720 nm and three sharp lines centered at 697, 700 and 701 nm.

Excitation by CW laser with 785 nm revealed IR luminescence lines which evidently may be ascribed to trivalent REE, such as Pr, Ho, Nd, Er and Yb (Gaft).

Best localities for fluorescence (*):

• Lake Jaco, Chihuahua Mexico;
• Jeffrey Mine, Asbestos, Les Sources RCM, Estrie, Québec, Canada (pink under LW);
• Lelatema Mountains, near Arusha, Tanzania (colorless crystal luminescent in strong apricot color under SW);
• variety hessonite from Beaver Mine, Thetford Mine, Quebec, Canada (bright orange under SW);
• King mine, Thetford Mines, Les Appalaches RCM, Chaudière-Appalaches, Québec, Canada (orange SW);
• Sierra de Cruces, Mun. de Sierra Mojada, Coahuila, Mexico;

(*)The data are not exhaustive and are limited to a few remarkable localities for fluorescence

Bibliographic reference for luminescence:

• The Henkel Glossary of Fluorescent Minerals, Dr. Gerhard Henkel, Published by the FMS, 1989 ,
• Fluorescence: Gems and Minerals Under Ultraviolet Light, Manuel Robbins, 1994, Geoscience Press, ISBN 0-945005-13-X ,
• Luminescence Spectroscopy of Minerals and Materials, M. Gaft, R. Reisfeld, G. Panczer, Springer Editor, ISBN: 10 3-540-21918-8 ,

Reference for luminescence on the Internet:

Mineralogical reference on the Internet:

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

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

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