Garnet, the Birthstone for January

Garnet is commonly known for it's red variation, but the term garnet is used to describe a much broader group of minerals. Garnet is present in a broad selection of colors: deeply saturated purplish reds, reds, greens, oranges, pinkish oranges, and even some blues. Many of these colors are rare. The normal red garnet is typically pyrope but may also be almandine garnet.

Garnet minerals

• Almandine - is the most commonly found garnet, but is usually opaque. When transparent or translucent crystals are found they make beautiful gems. Almandine is dark in color being typically a deep red to reddish brown. Occassionally almandine may exhibit a four star pattern, in a phenomena known as asterism. Mozambique is a prime source for fine quality almandine garnets.
• Andradite - is the name for the mineral group, and is not used to refer to the gem varieties. As a mineral it is typically found as an opaque material unfit for use. The gems produce a high lustre for which it is prized.
  • Demantoid - a very rare garnet gem that is an olive green color. The original source of demantoid was from Russia and these gems invariably contained small horsetail inclusions of asbestos. The most sought after demantoids are large and exhibit a characteristic high lustre and fire.
  • Melanite (Black Garnet) - a popular opaque, black variety that has a very reflective, submetalic luster.
  • Topazolite - a yellow to orange yellow variety that is rarely found in large enough size to be cut for jewelry use.
• Grossular - a garnet mineral that in it's pure form is colorless. However due to impurities is found in numerous colors: white, red, green, yellow, orange, brown, pink, purple, and gray.
  • Gooseberry - green to greenish-brown light in color
  • Hessonite - orange to orange-brown
  • Hydrogrossular - technically made up of a different chemical composition than regular grossular, it is widely grouped as a variety of grossular garnet. It is typically found as in massive veins of opaque white to light green color, and occassionally with pink coloration. Due to visual similarites with the highly prized Jade, it has been referred to using Jade misnomers: Transvaal Jade, garnet jade etc.
  • Imperial - light pink in color
  • Leuco - the colorless variety
  • Mint - a mint green variety
  • Raspberry - raspberry-red color
  • Rosolite - similar to Raspberry but lighter in tone
  • Tsavorite - a green variety that has gained popularity for it's rich green that is reminiscent of emeralds.
• Spessartite (or Spessartine) - orange to orange-red in color.
  • Malaia - from the Umba River Valley in Tanzania and Kenya. It is reddish-orange.
  • Mandarin - bright orange to orange-red from Namibia and Mozambique.
  • Tangerine - light orange to orange-yellow in color
• Pyrope - this is the most common garnet found as a gemstone. It is a dark red color.
  • Color-Change - an intermediate garnet mixture of pyrope and spessartite. It shows a different color in natural light (sunlight) and incandescent light. The color in daylight is light brown, yellow, or green, and then in artificial light is pink or purple. An rare variation may show a blue color.
• Rhodolite - is an intermediate mineral sharing the chemical compostion of almandine and pyrope (typically more pyrope composition than almandine). It exhibits a rose-red to violet color.
• Uvarovite - a rare garnet mineral, that is typically found is minute crystal size. Only found in a deep green color.

Birthstones and Anniversaries

The traditional red garnet is the birthstone for January, although other garnets colors may be substituted if desired. It is also the gem of the second anniversary.

Physical qualities

• Chemical Composition: 
  • Almandine - Fe₃Al₂(SiO₄)₃
  • Andradite - Ca₃Fe₂(SiO₄)₃
  • Grossular - Ca₃Al₂(SiO₄)₃
  • Pyrope - Mg₃Al₂(SiO₄)₃
  • Rhodolite - (Mg, Fe)₃Al₂(SiO₄)₃
  • Spessartine - Mn₃Al₂(SiO₄)₃
  • Uvarovite - Ca₃Cr₂(SiO₄)₃
• Refractive Index: 1.714-1.888
• Birefringence: None. Garnet is one of the few gems that is singly refractive.
• Specific Gravity: 3.47-4.15
• Mohs Hardness: 6.5-7.5

Buying Tips

Color: Garnets (pyrope and rhodolite) are very common. Look for intense, vivid color. Rich color should be available for most varietie, however the green gems Tsavorite and especially Demantoid are highly prized. These colors will require a premium.
Clarity: The red garnets: Almandine, Pyrope and Rhodolite, should be eye-clean. The orange garnets in the Spessartite and Hessonite series will invariably have inclusions that will be visible to the eye.
Cut: Red garnets will be readily available in all shapes and sizes. Other shapes will be more limited, particularly the green varieties.
Carat Weight: The red garnets are common in large sizes and so value does not rise dramatically. However in the more unusual forms the value will increase dramatically as size increases.

Read more at the GIA Garnet page.