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Garnet Gemstone, A Large Colorful Family

January 01, 2019

Garnet Gemstone, A Large Colorful Family

Garnet Gemstone is not a single mineral, is the name of a group which has a rich variety of color: red, orange, green, yellow, purple, pink, brown and even blue. 
Within of this group, we can find beautiful and affordable garnet stones and other more exclusive and expensive.

Garnet Gemstone is the name for a group of related mineral species. The group of garnets are formed by two isomorphic series (same structure but different composition).

The name is derived of the word “granum” or “granatum”, (pomegranate; for its resemblance to the seed of this fruit).

Versión Española

Contens

  1. Garnet Color
  2. Garnet Cut & Sizes 
  3. Garnet Stone Clarity & Inclusions
  4. Genesis & Origin of Garnets
  5. January Birthstones
  6. Enhancements and Synthesis of Garnets
  7. General Description Physical & Optical Properties of Garnets

GARNET COLOR

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Garnet Gemstone are available in a rich variety of beautiful and radiant colors, the most common is the red garnet; but we can also find greens, oranges, yellows, purples, pinks, browns and even blues.

Garnets can exhibit the Color Change phenomenon and asterism.  

Color Change Garnet 0.63 ct

  • Almandine - Red - Brown (colored by Fe)
  • Pirope - Red (colored by Cr)
    •      Rhodolite - variety of Almandine & Pirop - Pink-red (colored by Fe)
  • Spessartine - Orange (colored by Mn)
  • Grossular - Varieties:
    •       Tsavorite - Green (colored by V)
    •       Hessonite - Cloudy Orange-Yellow (colored by Fe)
    •       Hydrogrossular - Green (Cr), Pink (Mn), white, grey ,blue.
  • Andradrite. Varieties:
    •       Demantoid Garnet - Green (Cr)
    •       Topazolite - Yellow (Fe)
    •       Melanite - Black (Ti replacing part of Fe)
  • Uvarovite - Green (Cr)
Rhodolite Garnet 11.03 ct
The most expensive color varieties are Tsavorite garnets, Demantoid garnets, Spessartites (Mandarin Garnet) and Change Color Garnets.  

Mali Garnet 4.54 ct

GARNET CUT & SIZES

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Transparent garnets can use any style of cut. The most common styles are standard shapes (oval, emerald, trillion, round, etc.) Translucent and opaque garnets are cut into cabochon, carvings and beads. Garnets with cat eye effect or asterism also are cut into cabochon.

Pair Mandarin Spessartite Garnets cabochon cut

Green Hydrogrossular ("Transvaal Jade") is cut into cabochon or imitating the jade pieces. 

Garnets are available in large sizes, however Demantoid and Tsavorite are common small sizes, this two stones are the most expensive of all garnets. 

Tsavorite garnets is cut trying to maximize the weight retention of the rough. Demantoid Garnets is often cut into round, brilliant and cushion shapes (which facilitates viewing of its FIRE).

 Pair Spessartite Garnets

 

GARNET STONE CLARITY & INCLUSIONS

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Almandine, Pyrope, Rhodolite (red garnets) will show eye-visible inclusions unlike the Spessartine, Hessonite (orange garnets) which will show eye-clean inclusions .

Grossular is usually translucent

 

Typical inclusions: Solid Inclusions, healed fracture, liquid inclusions, etc. Demantoid might have eye-visible inclusions called horsetails (chrysotile fibers). Hessonite garnet often has a turbulent inner appearance and is typically heavily included.

View our Inclusions Gallery - Beauty is Inside

Solid Inclusions in Spessartite Garnet

 

GENESIS & ORIGIN OF GARNETS

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Almandine: The most common of the garnets group of metamorphic origin. Main deposits in India (Rajasthan), Sri Lanka, Tanzania, Madagascar, Brazil, USA, etc. 

Pirope: Is commonly associated to diamond mines and kimberlites. Russia, South Africa, Tanzania, Botswana, Australia, Sri Lanka. Brazil, Madagascar, etc. 

     Rhodolite: EEUU (North Carolina), Sri Lanka,
     India, Zimbabwe, Tanzania, Brazil, Kenya,
     Madagascar, Malawi. 

Sperssatina: Pegmatites, igneous rock or metamorphic rock. Sri Lanka, Madagascar, Myanmar, Brazil, Namibia, Nigeria, Afghanistan, etc.

Grossular: Metamorphic rocks.

     Hessonite: Sri Lanka, Brazil, Siberia, Canada,
     USA.
     Tsavorite: Tsavo Park, Kenya, Tanzania.
     Hidrogrossularia: Transvaal (North
     Africa), Canada, USA, China, Myanmar. 

Andradite: Metamorphic rocks.

     Demantoid: Russia, Zaire, Madagascar, Iran,
      Afghanistan, Italy.
     Topazolite: Italy, Kenya, USA, Romania.
     Melanite (volcanism): Italy (Vesuvius), France,
      USA, Brazil.

Uvarovite: Metamorphic rocks. Russia (Urals), USA (California), Canada, Finland, India.

Demantoid Garnet

 

JANUARY BIRTHSTONES

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January Birthstone Garnets

The powers attributed to garnet are varied. To bring peace, prosperity, health, friendship, security.

Garnet is the Birthstone of January, the zodiacal stone of Aquarius and the gem that is usually gives for the second wedding anniversary.

More information about Birthstones.

 

ENHANCEMENTS AND SYNTHESIS OF GARNETS

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Enhancements:

Garnets are usually not enhanced.

Some Demantoid low temperature heat treated to improve color.

Synthesis:

Non-commercial.

Imitations (Glass, YAG, GGG, etc)

 

GENERAL DESCRIPTION PHYSICAL & OPTICAL PROPERTIES OF GARNETS

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Inclusions in Color Change Garnet
Needles (Solid Inclusions) in Change Color Garnet

 

Inclusions in Spessartite Garnet 9.24 ct
Healed fractures inclusions in Spessartite Garnet

 

Inclusions in Mali Garnet
Solid inclusions and healed fractures in Mali Garnet

 

Inclusions in Mali Garnet Round Cut
Internal tension in Mali Garnet

 

Inclusions in Spessartite Garnet
Healed fractures and liquid inclusions in Spessartite Garnet

NESOSILICATES

Formula:          X3 Y2 (SiO4)3
X - Divalent cations = Ca2+, Mg2+, Fe2+ o Mn2+
Y - Trivalent cations = Al3+, Fe3+ o Cr3+

 

Pyralspite garnets - aluminium in Y site

  • Almandine (deep red)
  • Pyrope (red)
  • Spessartine (orange)

Ugrandite group - calcium in X site

  • Grossular
    • Tsavorite (green)
    • Hessonite (orange/yellow)
  • Andradite
    • Demantoid (green)
    • Topazolite (yellow)
    • Melanite (black)
  • Uvarovite

Isomorphous series:

  • Rhodolite: Pyrope - Almandine
  • Umbalite: Pyrope - Spessartine (Change Color Garnet)
  • Spessartine - Almandine
  • Pyrope - Grossular
  • Mali Garnet: Grossular - Andradite

 

  • Crystal system: Cubic.
  • Habit: Trapezohedral, dodecahedral
  • Hardness (Mohs): 7 - 7.5 (Andradite ; 6.5 -7)
  • Fracture: Sub-Conchoidal
  • Transparency: Transparent, translucent, opaque
  • Streak: White.
  • Lustre: Vitreous, resinous, subadamantine.
  • Dispersion: 0.022 - 0.057 (demantoid)
  • Density: 3.40 to 4.32 g/cm3
  • Optic nature: Isotropic
  • Refractive index: 1.73 - 1.89
  • Birefringence: No. Singly refractive.
  • Pleochroism: No
  • Fluorescence: Mostly inert.
  • Absorption spectrum: Variable.

 




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