Gahnite

Big Photo

Bahia, Brazil
0.87 carats

Gahnite is named after J.G. Gahn, a Swedish chemist and mineralogist, who discovered the mineral. It was first described in 1807 for an occurrence in the Falu mine, Falun, Dalarna, Sweden.

Gahnite is a rare mineral belonging to the Spinel group. It has the same structure as Spinel but different chemistry (zinc).

Gahnite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
 

Gahnite Gemstones by Size

This table shows distribution of Gahnite gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
Contributed photos
Lightest:0.20 cts
Heaviest:1.17 cts
Average:0.66 cts
Total photos:6
Do you have a larger Gahnite? Why not upload a photo?
0.20ct to 0.30ct0.30ct to 0.39ct0.39ct to 0.49ct0.49ct to 0.59ct0.59ct to 0.69ct0.69ct to 0.78ct0.78ct to 0.88ct0.88ct to 0.98ct0.98ct to 1.07ct1.07ct to 1.17ct
General Information
Chemical Formula
ZnAl
 
2
O
 
4
Michael O’Donoghue, Gems, Sixth Edition (2006)
Photos of natural/un-cut material from mindat.org
Physical Properties of Gahnite
Mohs Hardness7.5 to 8
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
Specific Gravity4.00 to 4.62
Walter Schumann, Gemstones of the world (2001)
More from other references
Optical Properties of Gahnite
Refractive Index1.790 to 1.818
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
Optical CharacterIsotropic
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Anomalous double refraction
Colour
Colour (General)Red-violet, different blue shades, green or blackish.
Walter Schumann, Gemstones of the world (2001)
More from other references
Causes of ColourBlue, Fe2+ in tetrahedral coordination
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTransparent
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
Crystallography of Gahnite
Crystal SystemIsometric
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
HabitOctahedra
Michael O’Donoghue, Gems, Sixth Edition (2006)
Geological Environment
Where found:Natural gahnite occurs as an accessory mineral in granites and granite pegmatites.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Further Information
Mineral information:Gahnite information at mindat.org
Significant Gem Localities
Nigeria
 
  • Kaduna
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 413
Sri Lanka
 
  • Sabaragamuwa Province
    • Ratnapura District
      • Ratnapura
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