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Gemstone Properties:   Achroite   Actinolite   Alexandrite   Almandine   Amber   Amethyst   Ametrine   Andradite   Andalusite   Apache Tear   Apatite   Aquamarine   Axinite   Barite   Benitoite   Beryl   Bixbite   Bytownite   Calcite   Cassiterite   Cerussite   Chrysoberyl   Citrine   Clinozoisite   Cordierite    Corundum   Cubic Zirconia   Danburite   Demantoid   Diamond   Diopside   Dravite   Ekanite   Elbaite   Emerald   Epidote   Euclase   Feldspar   Fluorite   GGG   Garnet   Goshenite   Gypsum   Hauynite   Heliodor   Hiddenite   Indicolite   Idocrase   Iolite   Kornerupine   Kunzite   Kyanite   Labradorite   Moldavite   Morganite   Obsidian   Opal   Orthoclase   Padparadschah   Peridot   Petalite   Piemontite   Phenacite   Prasiolite   Quartz   Rhodochrosite   Rhodolite   Rubellite   Ruby   Sapphire   Scapolite   Scheelite   Selenite   Sinhalite   Sphalerite   Sphene   Spinel   Spodumene   Schorl   Spessartite   Sunstone   Tanzanite   Topaz   Topazolite   Tourmaline   Tektite   Tsavorite   Verdelite   Vesuvianite   Wulfenite   YAG   Zincite   Zircon   Zoisite  

Garnet (various calcium and aluminum silicates)

Color: Red, brown, orange, yellow, green, blue, violet, colorless and black.

Cleavage: Imperfect

Fracture: Subconchoidal, usually brittle.

Heat sensitivity: Low to none, but tiny flaws such as cracks and bubbles can be exacerbated with heat.  Rhodolite seems to be the most heat sensitive of the garnets.

Pleochroism: None

Birefringence (double refraction): Only in rhodolite.

Crystal structure: Isometric, rhombic, dodecahedron.

--------Pyralspite Subgroup:

Pyrope (magnesium aluminum silicate - occasionally contains chromium and usually some iron colorants.)

Color: Intense deep red.

Moh’s hardness: 7-7.5

Refractive index: 1.73-1.76

Critical angle: 35°

Specific gravity: 3.65-3.8

Dispersion: Moderately high (.022-.023)

Almandite (iron aluminum silicate - iron is the red colorant.)

Color: Deep red with a wine to brown undertone.

Moh’s hardness: 7.5

Refractive index: 1.78-1.83

Critical angle: 34.5°

Specific gravity: 3.95-4.25

Dispersion: Moderately high (.024-.027)

Spessartite (magnesium aluminum silicate - manganese is the orange colorant.)

Color: Orange, red to brown.

Moh’s hardness: 7-7.5

Refractive index: 1.795-1.815

Critical angle: 33.5°

Specific gravity: 4.12-4.2

Dispersion: Moderately high (.027)

Rhodolite (combination of pyrope and almandine - iron is the purple colorant.)

Color: Rose-red, raspberry to violet.

Moh’s hardness: 7-7.5

Refractive index: 1.75-1.77

Critical angle: 34.5°

Specific gravity: 3.95-4.25

Dispersion: Moderately high (.023-.027)

            Birefringence (double refraction): None to slight.

--------Ugrandite Subgroup:

Grossular (calcium aluminum silicate)

Types/Color:

  • Tsavorite - Green - vanadium is the green colorant.

  • Leuco garnet - Colorless

  • Hessonite - Brown-orange, peachy-pink - manganese is the orange/yellow colorant.

Moh’s hardness: 7

Refractive index: 1.78-1.83

Critical angle: 34.5°

Specific gravity: 3.95-4.25

Dispersion: Moderately high (.024-.027)

Andradite (calcium iron silicate)

Types/Color:

  • Demantoid - Green, yellow-green to yellow-brown - chromium and iron are the green colorants.

  • Topazolite - Lemon-yellow

  • Melanite - Opaque black

Moh’s hardness: 6.5-7

Refractive index: 1. 85-1.899

Critical angle: 32

Specific gravity: 3.82-3.85

Dispersion: Very strong (.057)

Birefringence (double refraction): None to slight.

Cutting: Pre-polishing with a 1200 Nubond or a 3000 standard lap may cause orange peel which makes polishing difficult.

Polishing: Alumina on most common polishing laps.  50,000 diamond on most polishing laps, and 100,000 on ceramic.

Comments: Garnet does not always form in one of the above types.  Many garnets are a mix of different types.  For example Mali garnet, is a combination of andradite and grossular.  Dematoid (andradite) is the most valuable green garnet, and is extremely rare.  Most green garnet is tsavorite (grossular), which is still quite valuable.  A recent find of garnet has photochroic (color change) properties.

Gemstone Properties:   Achroite   Actinolite   Alexandrite   Almandine   Amber   Amethyst   Ametrine   Andradite   Andalusite   Apache Tear   Apatite   Aquamarine   Axinite   Barite   Benitoite   Beryl   Bixbite   Bytownite   Calcite   Cassiterite   Cerussite   Chrysoberyl   Citrine   Clinozoisite   Cordierite    Corundum   Cubic Zirconia   Danburite   Demantoid   Diamond   Diopside   Dravite   Ekanite   Elbaite   Emerald   Epidote   Euclase   Feldspar   Fluorite   GGG   Garnet   Goshenite   Gypsum   Hauynite   Heliodor   Hiddenite   Indicolite   Idocrase   Iolite   Kornerupine   Kunzite   Kyanite   Labradorite   Moldavite   Morganite   Obsidian   Opal   Orthoclase   Padparadschah   Peridot   Petalite   Piemontite   Phenacite   Prasiolite   Quartz   Rhodochrosite   Rhodolite   Rubellite   Ruby   Sapphire   Scapolite   Scheelite   Selenite   Sinhalite   Sphalerite   Sphene   Spinel   Spodumene   Schorl   Spessartite   Sunstone   Tanzanite   Topaz   Topazolite   Tourmaline   Tektite   Tsavorite   Verdelite   Vesuvianite   Wulfenite   YAG   Zincite   Zircon   Zoisite  
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