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Demantoid (a variety of Andradite)
Current inventory:  0 gems
 

Chemistry:  Ca₃(Fe³⁺)₂(SiO₄)₃ + Cr

Discovered in 1868;   IMA status: Valid: Andradite (pre-IMA; Grandfathered).
Demantoid Garnet was named by Nils Gustaf Nordenskiøld from the archaic German word "Demant" which means "diamond" in allusion to its very high brilliance resembling that of Diamond.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/A.08-110

Nickel-Strunz 10th Ed. ID:

9.AD.25

9 : SILICATES (Germanates)
A : Nesosilicates
D : Nesosilicates without additional anions; cations in [6] and/or greater coordination
25 : Garnet Group

Crystal Data

Crystallography:

Isometric - Hexoctahedral

Crystal Habit:

Commonly well-crystallized dodecahedra, trapezohedra, or combinations, to 5 cm. Also granular to massive.

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

Uneven to Conchoidal

Tenacity:

Brittle

Hardness (Mohs):

6.5 - 7.0

Density:

3.82 - 3.89 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Greenish Yellow, Green, Emerald Green, Dark Green

Transparency:

Transparent, Translucent

Luster:

Adamantine, Resinous, Dull

Refractive Index:

1.887  Isotropic

Birefringence:

0.000 (Isotropic)

Dispersion:

0.057 (high)

Pleochroism:

None

Other:

Weakly Anisotropic

Occurances

Geological Setting:

In skarns from contact metamorphism of impure limestones and calcic igneous rocks. Chlorite schists and serpentinites. Alkaic igneous rocks.

Type Locality:

Telyanskai River, Kemennya Teliyana, Nizhne-Tagil'skoye (Mednorudyanskoye) Cu Deposit, Nizhnii Tagil, Sverdlovskaya Oblast', Urals Region, Russia.

Year Discovered:

1868 (Andradite)

View mineral photos:

Demantoid Mineral Photos and Locations

More Information

Mindat.org (Demantoid)
Mindat.org (Andradite Garnet)
Webmineral.com (Andradite Garnet)

Demantoid is a variety of Andradite Garnet which is a member of the Garnet Group of minerals that includes Almandine, Andradite, Grossular, Pyrope, Spessartine and Uvarovite. All Garnets fall into these basic varieties and some Garnets are a combination of two. The Garnets are a complex family of minerals all with similar crystalline structures but varying greatly in chemical composition and properties. Demantoid is from the Andradite variety and is colored deep green by chromium. Topazolite is the yellow variety of Demantoid Garnet. The dispersion of Andradites is the highest of all Garnets and gems of this variety have tremendous fire. Demantoid from Russia is identified by its "horse-tail" inclusions of byssolite (fibrous amphibole). Demantoid is available from several sources around the world but most prized from the Urals Region of Russia.

Demantoid Garnet was named by Nils Gustaf Nordenskiøld from the archaic German word "Demant" which means "diamond" in allusion to its very high brilliance resembling that of diamond. The name Andradite is named after the Brazilian mineralogist José Bonifácio de Andrada e Silva (1763-1838) (1763-1838). The name Garnet comes from the Latin word granatus meaning grain. This is from the comparison of garnet grains in rock looking like the dark red seeds of the Pomegranite fruit scattered on the ground.
 

  
Demantoid Garnet gems for sale:

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