Gahnite | Gemopedia

Ranging from dark green to black in color, gahnite is a rare member of the spinel group. It was first discovered in Sweden 1807 and named in honor of Swedish chemist J.G. Gahn, who is credited with the discovery of manganese. While highly prized by mineral collectors for its octahedral crystal formation, gahnite is on occasion cut into faceted gems.
Alternate
Names
Zinc Spinel
Colors
Red-Violet, Blue, Green, Black

Gahnite Classification

Common Name

Gahnite

Species

Gahnite

Variety

Colors

Red-Violet, Blue, Green, Black

Alternate Names

Zinc Spinel

Gemstone Groups

Spinel

Key Separations

OTL RI, appearance and no dispersion.

Comments

Gahnite belongs to the spinel group but has a zinc in its chemistry.

Gahnite Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.8
Tolerance:(+0.005/-0.010)

Birefringence

Optic Character

NA

Optic Sign

Polariscope Reaction

Singly Refractive (SR)

Fluorescence

SWUV:
LWUV:

CCF Reaction

Pleochroism

None

Dispersion

Comments

Gahnite Chemistry & Crystallography

Chemical Name

zinc aluminum oxide

Chemical Formula

ZnAl2O4

Synthesis

Crystal System

Cubic

Classification

Oxide

Nature

Natural

Crystallinity

Crystalline

Comments

Gahnite Characteristic Physical Properties

Hardness

7.5-8

Streak

Gray-White

Specific Gravity

4.4-4.63 Typical:4.55

Toughness

Poor

Inclusions

Luster

Vitreous

Stability

Fracture

Uneven

Cleavage

None

Comments

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