Garnet

saf-ahyuh r
January Birthstone

Though they all have the same crystal structure (cubic, like diamond and spinel), garnet is an entire group of minerals that vary in their chemical composition, resulting in a variety of gems featuring different colors and properties. Though some varieties of red garnet are common and found on nearly every continent on Earth, other garnets like orange spessartite, green demantoid and tsavorite, are much less abundant. There are more than 20 garnet species, but the five most important include pyrope and almandite (the combination of which creates rhodolite), spessartite, grossularite or grossularite (which includes hessonite and tsavorite), and andradite (which includes demantoid). Garnets of all species are the birthstone for January, so January babies aren't limited to the well-known red varieties.

Garnet Classification
Common Name Garnet
Species Garnet
Garnet Optical Properties
Transparency Transparent - Semitranslucent
Dispersion Strength: Moderate Fire Value: 0.024
Refractive Index Over The Limit 1.78-1.82
Tolerance:(+0.030/-0.030)
Optic Character NA
Optic Sign NA
Polariscope Reaction Singly Refractive (SR) With ADR
Fluorescence SWUV: Inert
LWUV: Inert
Pleochroism None
Garnet Characteristic Physical Properties
Hardness 7-7.5
Specific Gravity 3.930-4.300 Range:0.25/-0.12 Typical:4.05
Toughness Good
Inclusions Garnet is a type II clarity stone. Stones are often found with needles that intersect at 70º to 110º angles. Zircon crystals are commonly seen with strain halos. Irregular or rounded crystals can also be found.
Luster Vitreous
Stability Good
Fracture Conchoidal
Cleavage None
Garnet Chemistry & Crystallography
Chemical Name Iron Aluminum Silicate
Chemical Formula Fe3Al2(SO4)3
Crystal System Cubic
Chemistry Classification Silicate

Garnet Colors

  • Brown Garnet Brown
  • Red Garnet Red
  • Orange Garnet Orange
  • Green Garnet Green

Garnet Spectra

Garnet Spectra
HYDORGROSSULAR GARNET

Color due to chromium. With translucent material cut en cabochon light does not penetrate far and often a thin edge is best to obtain sufficient transmission to observe a spectrum. Only a vague absorption band may be detected centered about 600nm. a narrower stronger one at 640nm. and a stronger one at 675nm. this being difficult to resolve as it has very little transmission

Garnet Spectra
HYDRO-GROSSULAR GARNET

Color mainly due to manganese. Weak absorption in the areas 505nm. and 527nm. Weak general absorption of the yellow

Garnet Spectra
TERBIUM GALLIUM GARNET

Color due to rare earth element. The dominant feature is a very strong sharp line at 485nm. with two very delicate faint lines, each one about 5nm. on either side of this. There is also a weak general absorption of the yellow centered at 565nm

Garnet Spectra
SAMARIUM GALLIUM GARNET

Color due to rare earths. Color due to rare earth element, possibly erbium. Strong sharp absorption lines of various widths in the red, green, blue and violet areas depict a typical rare earth spectrum.

Garnet Spectra
SAMARIUM GALLIUM GARNET

Color due to rare earths. Strong sharp absorption lines of various widths in the red, green, blue and violet areas depict a typical rare earth spectrum. Because of the intense orange color of this crystal the spectrum shows a solid broad band centered at 500nm. Emission lines in blue, violet.

Garnet Spectra
GARNET TOP DOUBLET

Color due to selenium. The red glass pavilion is responsible for the body colour. The broad absorption band in the green is of moderate width in keeping with the light purplish hue This extends a little further to the shortwave side with additional absorption at 505nm. due to absorption by the garnet top

Garnet Spectra
GARNET TOP DOUBLET

Color due to selenium. A relatively low selenium content in the glass pavilion is sufficient to cause a fairly strong and broad absorption band to cover most of the green. This masks any indication of the iron band which may be present at 505nm. due to the thin garnet top.

Garnet Spectra
GARNET TOP DOUBLET

Color due to iron and selenium. The strength and extent of the absorption band centered at 540nm. in the green is determined by the depth of color in the red glass used in the doublet. Any absorption attributed to the almandine garnet top will depend on the thickness of this and is often masked by the absorption of the glass base. However, the almandine band at 505nm. can sometimes be detected, if not on its own, then by an extension of the broad band further into the blue and a further almandine line at 462nm.

Garnet Spectra
GARNET TOP DOUBLET

Color due to pink glass pavilion.The section of garnet forming the table on the crown of this stone is extremely thin and does not play any part in the overall body color. Only very vague indications of the almandine bands can be detected, and the spectrum is dominated by the broad absorption band in the yellow green from the glass pavilion which is probably due to colloidal gold.

Garnet Spectra
GARNET TOP DOUBLET

Color due to iron and possibly manganese. A faint almandine spectrum is present due to the garnet crown. This is represented by the weak band at 505nm. and two even fainter ones centered at 527nm. and 576nm. Lines in the blue were difficult to detect and are possibly due to manganese in the yellow glass pavilion

Garnet Spectra
GARNET TOP DOUBLET

Color due to cobalt in glass pavilion. What appears at first to be a typical cobalt spectrum is more complicated as the bands due to the almandine component in this composite stone are incorporated in the spectrum. First the almandine iron line is seen at 505nm. followed by another weak iron line at 527nm. which, together with the cobalt band, increases the width of the absorption in the green. Another narrow band at 576nm., again due to the almandine garnet crown, is seen to the shortwave side of the 590nm. cobalt band. Another weaker almandine band is seen at 617nm. before the cobalt band at 655nm.

Garnet Spectra
GARNET TOP DOUBLET

Color due to cobalt in glass pavilion. Because the garnet section is thicker than in some doublets, the absorption due to the almandine iron bands is more intense and broader. This is evident in the broad absorption from 490nm. to 500nm.in the green and also in the other two absorption areas in the yellow and red. The almandine band at 617nm. more obvious than in the spectra of doublets with thinner almandine sections.

Garnet Spectra
GARNET TOP DOUBLET

Color due to glass pavilion. As the garnet component is an extremely thin slice with the join just below the table the garnet is too thin to produce any almandine lines in the continuous spectrum from the greenish blue glass pavilion.

Garnet Spectra
ROUGH GARNET

Color due to chromium. The spectrum of chrome pyrope garnet is dominated by a powerful absorption band centered at 570nm. In some cases, as here, a weak doublet may be detected in the red at 685/686nm. Also due to chromium. Only a trace of the line at 505nm indicates a very low iron content. Any indication of weak lines at 576nm and 527nm usually associated with almandine, have been masked by the broad central absorption. Total absorption occurs from 475nm again.

Garnet Spectra
GARNET

Color due to chromium and possibly manganese. This garnet is a dark purplish red in daylight with a color shift to dark brownish red in tungsten light. The low chromium content provides a moderately wide band centered about 570nm. This is followed on the short-wave side by two very weak lines at 527nm. and 505nm. due to a very low iron content. A vague band is also seen about 489nm. suggesting a little manganese may be present. Strong absorption from 470nm. masks any other lines which may be present due to manganese.

Garnet Spectra
GARNET

Color due to iron. An increase in iron produces a much stronger spectrum. A weak vague band can be detected at 617nm. The band at 576nm. is pronounced and those at 527nm. and 505nm have merged. After that almost total absorption sets in.

Garnet Spectra
GARNET

Color due to iron - very strong. The powerful absorption seen here is indicative of a high iron content. The band at 576nm. Is now about 20nm. wide and those at 527nm. and 505nm. have merged to give a block stretching almost 50nm. wide. The diffuse band at 617nm. is a little more evident and the line at 462nm. is broader and stronger.

Garnet Spectra
GARNET

Color due to iron. The moderate strength of the band at 505nm. indicates a possible member of the pyrope- almandine series. In this particular stone the other bands at 576nm. and 527nm. In the yellow green are weak and the two lines in the blue are vague suggesting a relatively small iron content

Garnet Spectra
GARNET. Pyrope - Spessartine

Color due to chromium and manganese. A weak band in the yellow-green area 573nm. and the two narrow bands in the blue 420nm & 430nm suggests a Pyrope - spessartine series.

Garnet Spectra
GARNET

Color due to manganese. The spectrum shows the two manganese lines at 462nm. and 489nm. but there is no evidence of the usual absorption due to iron at 505nm

Garnet Spectra
GARNET.(Pyralspite)

Color due to manganese. The band in the violet at 432 indicates the manganese content of spessartine. The absence of even a weak absorption at 505nm. suggests very little or no iron. The trade name may be Mandarin or Malaia Garnet

Garnet Spectra
GARNET – Spessartine

Color due to manganese Most garnets classified as Spessartine have a small iron content seen here as a weak vague band at 505nm. and a very faint one at 527nm. The darker bands centered at 462nm. and 489nm. are due to manganese and indicate a spessartine garnet. The strong absorption below 445nm. here masks another two lines due to manganese at 432nm. and 412nm

Garnet Spectra
GARNET. Pyrope - Almandine series

Color due to chromium and iron. A moderately strong band centered at 570nm. Due to chromium masks any indication of the usual almandine band normally seen at 576nm due to iron. However, a very slight transmission is enough to separate the iron band at 527nm. From the chromium band and is followed by the other weak iron band at 505nm. This may then be classed as a member of the pyrope-almandine series.

Garnet Spectra
GARNET Greenish Blue Color Change

Color mainly due to vanadium and chromium. This garnet from Sri- Lanka is part of the pyrope- spessartine series. The absorption band centered at 570nm; due to vanadium and chromium, is responsible for a color change to purplish red in tungsten light. The narrower bands at 463nm. and 489nm. are due to Fe2+ and Mn. respectively.

Garnet Spectra
GARNET - Andradite

Color due to iron. The considerable iron content does not allow transmission much beyond 500nm. as it absorbs all blue and violet light obscuring the band usually seen centered at 443nm.

Garnet Spectra
Garnet - Blue

Color due to vanadium. A pale shade of lavender blue garnet from the pyrope - spessartine series with few features in the spectrum. However, the faint absorption band in the yellow and the extensive transmission in the red is sufficient to create a color change to brownish pink in tungsten light. Lines often seen in the blue due to iron and manganese are obscured by the absorption which extends up to 460nm.

Garnet Spectra
GARNET

Color due to iron. Often the iron band centered at 443nm. in andradite garnet may extend to give a cut off about 460nm., but this dark brown variety only transmits light above 510nm. indicating a very high iron content, producing this deep color. This garnet comes within the grossular - andradite series known in the trade as "Mali garnet".

Garnet Spectra
GARNET Grossular - andradite

Color due to iron. A broad strong band centered at 443nm.in the deep blue

Garnet Spectra
GARNET

Color due to manganese As the orange hue deepens transmission in the deep blue and violet region is poor and absorption lines in this area are difficult to detect. Two lines of moderate strength due to manganese at 462nm. and 489nm. and lines at 505nm and 527nm. due to iron. The lines at 432nm. and 412nm. due to manganese are again masked by the strong general absorption in this area

Jewelry Television acknowledges the significant scientific contributions of John S Harris, FGA to the study of gemstone spectra and with deep appreciation to him, acknowledges the use of his images and related notes about gemstones and their spectra in the educational materials on this website.

Countries of Origin

Tanzania, United Republic Of; Afghanistan; Madagascar; Thailand; Austria; Mongolia; Mozambique; Pakistan; Morocco; Unknown; Mali; China; Russian Federation (the); Brazil; Nigeria; United States of America (the); Sri Lanka; Congo (the); Japan; Zambia; Kenya; Switzerland; French Polynesia; India; Canada; Norway; Namibia; Italy; Mexico; South Africa; Australia; Ethiopia

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Species/Variety

Almandine Garnet

Though they all have the same crystal structure (cubic, like diamond and spinel), garnet is an entire group of minerals that vary in their chemical composition, resulting in a variety of gems featuring different colors and properties. Though some varieties of red garnet are common and found on nearly every continent on Earth, other garnets like orange spessartite, green demantoid and tsavorite, are much less abundant. There are more than 20 garnet species, but the five most important include pyrope and almandite (the combination of which creates rhodolite), spessartite, grossularite or grossularite (which includes hessonite and tsavorite), and andradite (which includes demantoid). Garnets of all species are the birthstone for January, so January babies aren't limited to the well-known red varieties.

Almandine Garnet Garnet
Almandine Garnet Classification
Common Name Almandine Garnet
Almandine Garnet Optical Properties
Dispersion Strength: moderate fire Value: 0.024
Refractive Index Over The Limit 1.78-1.82
Tolerance:(+0.030/-0.030)
Fluorescence SWUV: Inert
LWUV: Inert
Almandine Garnet Characteristic Physical properties
Specific Gravity 3.93
Inclusions Almandite garnet is a type II clarity stone. Stones are often found with needles that intersect at 70o to 110o angles. Zircon crystals are commonly seen with strain halos. Irregular or rounded crystals can also be found.

Melanine

Melanite is an extremely rare opaque jet-black variety of andradite garnet. The high luster of this gem, when faceted, makes the stone look like black glass. Melanite was extremely popular in Victorian period mourning jewelry.

Melanine Garnet
Melanine Classification
Common Name Melanine
Melanine Optical Properties
Refractive Index Over the Limit 1.855-1.895
Fluorescence SWUV: Inert
LWUV: Inert
Melanine Characteristic Physical properties
Specific Gravity 3.7

Malaia Garnet

Discovered in the mid 1960's in Tanzania's Umba Valley, this red-orange to pink-orange variety of garnet was originally thought to be spessartite garnet. Actually a mixture of pyrope and spessartite, malaia garnets are lively gems that exhibit sparkling red flashes. Once discovered not to be spessartite, it soon became known by the Swahili word malaia, meaning "out of the family." Malaia garnets are available in numerous shades of orange, ranging from soft peach to intense reddish orange.

Malaia Garnet Garnet
Malaia Garnet Classification
Common Name Malaia Garnet
Malaia Garnet Optical Properties
Dispersion Strength: moderate fire Value: 0.022
Refractive Index 1.75-1.78
Fluorescence SWUV: Inert
LWUV: Inert
Malaia Garnet Characteristic Physical properties
Specific Gravity 3.78
Inclusions Malaia garnet is a type II clarity stone. Stones sometimes contains rutile, apatite and pyrite mineral inclusions and intersecting needles.

Hydrogrossular Garnet

Hydrogrossular garnet is typically translucent to opaque and is usually available as cabochons, but on rare occasion may be found as transparent, faceted gemstones. Generally seen as green to blue-green, pink, white, and gray, this gemstone may contain small dark gray to black inclusions and may look similar to jade if opaque. Hydrogrossular is a variety of grossular garnet where hydroxide partially replaces silica.

Hydrogrossular Garnet Garnet
Hydrogrossular Garnet Classification
Common Name Hydrogrossular Garnet
Hydrogrossular Garnet Optical Properties
Refractive Index 1.72-1.72
Tolerance:(+0.010/-0.050)
Fluorescence SWUV: Inert
LWUV: Inert
CCF Reaction Green: possibly pinkish
Hydrogrossular Garnet Characteristic Physical properties
Specific Gravity 3.15
Inclusions Might have black magnetite inclusions that resemble pepper.

Andradite Garnet

Andradite is a fairly abundant, although less-known, member of the ugrandite garnet species, which also includes uvarovite and grossularite. Andradite makes spectacular gems that display greater color dispersion than diamond.

Andradite Garnet Garnet
Andradite Garnet Classification
Common Name Andradite Garnet
Andradite Garnet Optical Properties
Dispersion Strength: strong fire Value: 0.057
Refractive Index Over the Limit 1.888-1.94
Fluorescence SWUV: Inert
LWUV: Inert
Andradite Garnet Characteristic Physical properties
Specific Gravity 3.81
Inclusions Andradite garnet is a type II clarity stone. Due to low mohs hardness stones might show surface abrasions or scratches.

Optical Phenomena

Star

Star garnet exhibits the optical phenomenon called asterism, a star-like pattern created on the surface of a gemstone when light encounters parallel fibrous, or needle-like, inclusions within its crystal structure. Light that strikes the inclusions within the gem reflects off of the inclusions, creating a narrow band of light. When two or more intersecting bands appear, a star pattern is formed. Depending on the crystal, the star may have four, six, or even twelve rays. When only one band forms, it is classified as a "cat's eye".

Star Garnet
Star Classification
Common Name Star
Star Optical Properties
Dispersion Strength: moderate fire Value: 0.026
Refractive Index 1.75-1.78
Fluorescence SWUV: Inert
LWUV: Inert
Star Characteristic Physical properties
Specific Gravity 3.74
Inclusions Pyrope-almandite garnet is a type II clarity stone. Needle like inclusions produce 4 to 6 rayed stars and will sometimes show both in well cut stones.Stones might have zircon crystals with stain halos and irregular rounded included crystals that might be zircon or apatite.

Star Almandine Garnet

Star almandite garnet exhibits the optical phenomenon called asterism, a star-like pattern created on the surface of a gemstone when light encounters parallel fibrous, or needle-like, inclusions within its crystal structure.Light that strikes the inclusions within the gem reflects off of the inclusions, creating a narrow band of light. When two or more intersecting bands appear, a star pattern is formed. Depending on the crystal, the star may have four, six, or even twelve rays. When only one band forms, it is classified as a "cat's eye".

Star Almandine Garnet Garnet
Star Almandine Garnet Classification
Common Name Star Almandine Garnet
Star Almandine Garnet Optical Properties
Dispersion Strength: weak fire Value: 0.024
Refractive Index Over The Limit 1.78-1.82
Tolerance:(+0.030/-0.030)
Fluorescence SWUV: Inert
LWUV: Inert
Star Almandine Garnet Characteristic Physical properties
Specific Gravity 3.93
Inclusions Almandite garnet is a type II clarity stone. Displays 4 or 6 rayed stars and sometimes well cut stones will show both. Stones are often found with needles that intersect at 70o to 110o angles. Zircon crystals are commonly seen with strain halos. Irregular or rounded crystals can also be found.

Rainbow Garnet

Also called "rainbow garnet," this gray to deep brown garnet displays phenomenal iridescence. The iridescence is caused by the way grossular and andradite garnet are mixed together in this single gem, forming a crystal structure that both scatters and traps light within the gem, creating a myriad of colors.

Rainbow Garnet Garnet
Rainbow Garnet Classification
Common Name Rainbow Garnet
Rainbow Garnet Optical Properties
Dispersion Strength: strong fire Value: 0.057
Refractive Index 1.888
Fluorescence SWUV: Inert
LWUV: Inert
Rainbow Garnet Characteristic Physical properties
Specific Gravity 3.81
Inclusions Iridescent andradite garnet is type II clarity stone. Iridescence is caused by twinning planes and occurs in parallel angled bands or patchy areas.

Color-Change

Color change garnets are among the rarest, most interesting of all gemstones. This phenomenal gem is in fact a mixture of garnet species. You can observe color change in this gem by viewing it interchangeably in natural and incandescent light.

Color-Change Garnet
Color-Change Classification
Common Name Color-Change
Color-Change Optical Properties
Dispersion Strength: moderate fire Value: 0.022
Refractive Index 1.75-1.78
Fluorescence SWUV: Inert
LWUV: Inert
Color-Change Characteristic Physical properties
Specific Gravity 3.78
Inclusions Color-change garnet is a type II clarity stone. Stones sometimes contains rutile, apatite and pyrite mineral inclusions and intersecting needles.

Cat's Eye

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case andradite garnet. The effect, when present, appears as a bright, narrow slit similar to the pupils in the eyes of your favorite feline. This phenomenon is caused by parallel fibrous or needle-like inclusions that interfere with the passage of light throughout the crystal, scattering and reflecting light back to the viewer as a thin line.Andradite garnet is relatively unfamiliar to the general public, but this species includes demantoid, melanite, topazolite and schorlomite. Garnets that feature a cat's eye are a rare occurrence and should be treasured.

Cat's Eye Garnet
Cat's Eye Classification
Common Name Cat's Eye
Cat's Eye Optical Properties
Dispersion Strength: strong fire Value: 0.057
Refractive Index 1.888
Fluorescence SWUV: Inert
LWUV: Inert
Cat's Eye Characteristic Physical properties
Specific Gravity 3.81
Inclusions Iridescent andradite garnet is type II clarity stone. Chatoyancy is caused by parallel needles. Due to the stones low mohs hardness it might have scratches and abrasions.
Tim Matthews

Author

Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.