Classification
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Mineral
Classification: |
Silicates |
Strunz 8th
Ed. ID:
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8/A.08-110 |
Nickel-Strunz 10th
Ed. ID:
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9.AD.25 |
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9 : SILICATES (Germanates) A : Nesosilicates D : Nesosilicates without
additional anions; cations in [6] and/or greater coordination 25 : Garnet
Group
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Crystal
Data
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Crystallography:
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Isometric
- Hexoctahedral |
Crystal
Habit:
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Commonly
well-crystallized dodecahedra, trapezohedra, or combinations,
to 5 cm. Also granular to massive.
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Twinning:
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None
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Physical
Properties
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Cleavage: |
None
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Fracture: |
Uneven
to Conchoidal
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Tenacity:
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Brittle
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Hardness
(Mohs): |
6.5 - 7.0 |
Density:
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3.82
- 3.89 (g/cm3) |
Luminescence:
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None |
Radioactivity:
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Not
Radioactive |
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Optical
Properties
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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
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Other: |
Weakly
Anisotropic
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Occurances
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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 |
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More
Information
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Mindat.org
(Demantoid) Mindat.org
(Andradite Garnet) Webmineral.com
(Andradite Garnet) |
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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 Nordenskiĝld 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. |