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Gahnite  (Zinc Spinel)
Current inventory:  1 gem
 

Gahnite

Chemistry:  ZnAl2O4

Discovered in 1807;   IMA status: Valid (pre-IMA; Grandfathered).
Gahnite is n
amed after the Swedish chemist and mineralogist, Johan Gottlieb Gahn (1745-1818), who discovered Gahnite and manganese.

 

Classification

   

   

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/B.01-40

 

4 : Oxides & Hydroxides
B : Oxides with metal : oxygen = 3:4 (spinel type M3O4 and related), Alumina-Spinels
01 : Spinel group, Spinel - Gahnite series

 

 

Crystal Data

   

   

Crystallography:

Isometric - Hexoctahedral

Crystal Habit:

Crystals typically octahedra, rarely as dodecahedra, may be modified, to 12 cm; also as exsolution lamellae in other minerals; granular, massive.

Twinning:

On [111] as both twin and composition plane, common

 

 

Physical Properties

   

 

Cleavage:

[111] Indistinct

Fracture:

Conchoidal also Irregular, Uneven

Tenacity:

Brittle

Moh's Hardness:

7.5 - 8.0

Density:

4.00 - 4.64 (g/cm3)

Luminescence:

None

Radioactivity:

Not Radioactive

 

 

Optical Properties

   

   

Color:

Dark Bluish Green, Grayish Green, Deep Green, Greenish Black, Bluish Black

Transparency:

Transparent to Translucent

Luster:

Vitreous (glassy)

Refractive Index:

1.82  Isotropic  (1.790 - 1.820 due to impurities)

Birefringence:

0.00  Isotropic

Dispersion:

n/a

Pleochroism:

n/a

 

 

Occurances

   

   

Geological Setting:

An accessory mineral in granites and granite pegmatites; in medium- to high-grade metamorphic rocks and metamorphosed base-metal sulfide deposits; in diasporites, formed by the low-grade metamorphism of bauxites; a detrital mineral in placers. Gahnite is found in zinc deposites at many localities worldwide.

Type Locality:

Falu mine, Falun, Dalarna, Sweden

Year Discovered:

1807

View mineral photos:

Gahnite Mineral Photos and Locations

 

 

More Information

   

   

 

Mindat.org
Webmineral.com

 

 


Gahnite is one of the rarer members of the Spinel group of minerals. It is found at many zinc deposites worldwide. Crystals are typically very small, included and just translucent to opaque, but faceted gems are very collectable due to their rarity and color. Current sources are Australia, Brazil, Germany, Italy, Namibia, Nigeria, Sweden, and in the USA in Sussex County, New Jersey, Carroll County, Maryland, Mitchell County, North Carolina and Fremont County, Colorado.
 

  
Gahnite gems for sale:

Gahnite-001

Gem:

Gahnite

Stock #:

GAHN-001

Weight:

0.8595 ct

Size:

9.51 x 5.54 x 2.52 mm

Shape:

Elongated Triangle

Color:

Deep Forest Green

Clarity:

SI2

Origin:

Bahia, Brazil

Treatment:

None (natural)

Price:

SOLD (but we have others)

Pictures are of the actual gem offered for sale.
Gem images are magnified to show detail.

Gahnite-001

A very rare and beautiful gem in an unusaul cut, an elongated triangle, with ideal color for Gahnite.


 

I love Sarah