Garnet

Garnet illustration

Garnet hardness on the Mohs scale is approximately 7- 7.5  – well suited for use in jewelry. Most garnets are clear from inclusions. Due to their relative hardness and clarity, most garnets can be faceted. Garnets occur in all colors except blue

The name ‘garnet’ comes from the Latin granatus, meaning “the pomegranate” – an ancient fruit whose seeds resemble the crystals of the most common variety of garnet – the pyrope. For centuries garnet necklaces were worn by pharaohs of Egypt, a popular sarcophagus-stuffer for the afterlife. The term carbuncle was often used in ancient times to describe red garnets. Carbuncle was thought to be one of the four precious stones given to King Solomon by God.

  • General composition: A3B2(SiO4)3, where Ca, Mg, Fe2+, or Mn2+ occupy the A site, and the B site contains Al, Fe3+, or Cr3+.
  • Garnet Specific gravity: 3.4 – 4.3 (almandine 3.95-4.32, pyrope 3.53-3.87, spessartine 3.80-4.25, andradite 3.70-4.18, grossular 3.56-3.71 and uvarovite 3.40-3.90)
  • Refractive index: 1.72-1.94 (almandine 1.75-1.83, pyrope 1.73-1.77, spessartine 1.79-1.81, andradite 1.86-1.94, grossular 1.72-1.80 and uvarovite 1.74-1.87)
  • Garnet Birefringence: 0.000-0.005 (almandine 0.000, pyrope 0.000, spessartine 0.000-0.004, andradite 0.000-0.005, grossular 0.000-0.005 and uvarovite 0.000-0.005)
  • Garnet Pleochroism: none
  • Garnet Hardness: 6.5 – 7.5
  • Garnet Luster: vitreous to resinous, 
  • Phenomena: chatoyancy due to minute asbestiform inclusions of pyroxene or amphibole, yielding a four-ray star when fashioned into a cabochon gem
  • Garnet Transparency: transparent to opaque
  • Garnet Cleavage: none
  • Garnet Fracture: conchoidal, somewhat brittle
  • Garnet Streak: white
  • Hydrous garnets may contain up to 8.5% H2O
  • Garnet Class: nesosilicates
  • Garnet Crystal system: isometric; 4/m bar3 2/m
  • Garnet Crystal habit: commonly forms as rhombic dodecahedrons, trapezohedrons, or a mixture of these two forms. Rarely as hexoctahedrons. Also as coarse or fine massive granular.

Pyralspite Garnet Group

  • Almandine Garnet: Fe3Al2(SiO4)3
  • Pyrope Garnet: Mg3Al2(SiO4)3
  • Spessartine Garnet: Mn3Al2(SiO4)3

Ugrandite Garnet Group

  • Andradite Garnet: Ca3Fe2(SiO4)3
  • Grossular Garnet: Ca3Al2(SiO4)3
  • Uvarovite Garnet: Ca3Cr2(SiO4)3

Less Common Garnet Species

  • Calderite: Mn3Fe3+2(SiO4)3
  • Goldmanite: Ca3V2(SiO4)3
  • Hydrogrossular: Ca3Al2(SiO4)3-x(OH)4x
  • Hibschite: Ca3Al2(SiO4)3-x(OH)4x (where x is between 0.2 and 1.5)
  • Katoite: Ca3Al2(SiO4)3-x(OH)4x (where x is greater than 1.5)
  • Kimzeyite: Ca3(Zr,Ti)2[(Si,Al,Fe3+)O4]3
  • Knorringite: Mg3Cr2(SiO4)3
  • Majorite: Mg3(Fe,Al,Si)2(SiO4)3
  • Morimotoite: Ca3Ti4+Fe2+(SiO4)3
  • Schorlomite: Ca3(Ti4+,Fe3+)2[(Si,Ti)O4]3
Leon Mege demantoid garnet illustration

Demantoid garnet illustrationOlive-green to emerald-green rare and highly desirable gem variety of Andradite Garnet. The famous “horsetail” inclusion is often an identification mark that increases the stone’s value. Demantoids rival the fire of green diamonds because they have high dispersion. In fact, they were called “Green diamonds” in the past. A large demantoid was the focal point of a 1910 short novel by Alexander Kuprin” The Garnet Bracelet.”

tsavorite illustration leon mege

Green to an emerald-green transparent variety of Grossular Garnet from Africa. It is very popular and commands high prices.

Spessartite/spessartine 

Orange to reddish-brown highly prized variety. Mandarin garnet, naturally occurring in a vivid orange color due to manganese in its composition. Mandarin usually originates from the African countries of Namibia and Mozambique. Tangerine Garnet is light orange to orange-yellow Spessartine Garnet, usually from Namibia and Mozambique.

Rhodolite

Pale pink to violet-colored variety form of Garnet. Its light rose-red color is more purplish than typical garnets. It is usually an intermediary variety between Pyrope and Almandine, though more closely towards Pyrope in composition.

It exhibits a different color depending on the light source is a hybrid of the Pyrope and Spessartite that displays a color change from a light brownish, yellowish, or greenish in daylight to a pink or purplish color in incandescent light.  A few rare specimens may even have a bluish color.

Light green to a light greenish-brown variety of Grossular Garnet.

Orange to an orange-brown, transparent variety of Grossular Garnet

Light pink, the transparent gem variety of Grossular Garnet.

Colorless, transparent variety of Grossular Garnet.

Garnet gemstone from the African country of Mali ranges in color from green to yellow to brown (though most often a greenish-yellow). The deposit of these Garnets was discovered in Mali in 1994, and this form of Garnet is a relatively new gemstone. The scientific classification of the Mali Garnets is not clearly identified; they can be either Grossular or Andradite, though they are usually an intermediary form closer in chemical structure to Grossular.

Colorless to black variety. Melanite is lustrous, opaque black or very dark red variety of Andradite Garnet.

Mint garnet illustration Leon Mege

Grossular Garnet with a light-mint-green color. Very refreshing. Also known as Merelani Mint Garnet, it is named for the region of Tanzania where it was first found. Merelani has a light bluish-green hue, unlike the rich green or yellowish-green hues of tsavorites and demantoids.

Malaya garnet illustration Leon Mege

Malaia or Malaya garnet is a variety of light to dark slightly pinkish-orange, reddish-orange, and yellowish-orange mixture of pyrope, almandine, and spessartine with a little calcium.

Reddish-orange form of Spessartite Garnet (or, more accurately, a mixture intermediary between Spessartite and Pyrope) originates in the Umba River Valley in Tanzania and Kenya. On occasion, the term is used as a synonym for Spessartite.

Red Garnet from the African country of Mozambique, which produces fine quality Garnet gemstones. Mozambique Garnet is usually Almandine, but may also be Pyrope.

Raspberry-red variety of Grossular Garnet.

Form of Almandine Garnet exhibiting asterism in the form of a four-ray star.

Yellow to a brownish-yellow variety of Andradite Garnet.

Dark red to a violet-red variety of garnet.

White, yellow, yellow-green, brownish-red, orange, or black garnet.

Very common, inexpensive blood-red variety of garnet. Widely used in costume jewelry and Bohemian-style jewelry sold everywhere in Prague.

Uvarovite garnet illustration

Uvarovite

The rarest bright green garnet variety, so rare you can find it only in museum collections.

Garnet’s healing properties (insurance is not accepted): Garnet is a birthstone for January. Garnet is a 2nd Anniversary gemstone. Garnet represents love and commitment.  It is said to revitalize feelings and enhances relationships by bringing warmth, devotion, understanding, trust, sincerity, and honesty.  Said to control anger, although never scientifically tested.

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