Garnet Jewelry and Gemstone Information

Garnet

January’s Birthstone

Garnet Information

Garnet comes from the Latin word, “granatus” which means grain. That is because many garnet deposits are small grains of red crystals in or on their host rock.

Physical Properties

The garnets have no cleavage but display a conchoidal fracture and are somewhat brittle and tend to chip easily. The luster is vitreous, inclining to resinous in grossular, andradite, and some almandines. The hardness is 6.5-7.5 in grossular and uvarovite; 6.5-7 in andradite; and 7-7.5 in the pyralspite series.

Garnets are all isometric, and crystals show the common forms in this crystal system, such as the trapezohedron and dodecahedron. Interestingly, the most common isometric forms, the cube and octahedron, are extremely rare in garnet crystals. Garnets may also be massive, granular, and in tumbled pebbles.

Colors:

Uvarovite: dark green.

Grossular: colorless, white, gray, yellow, yellowish green, green (various shades: pale apple green, medium apple green, emerald green, dark green), brown, pink, reddish, black.

Andradite: yellow-green, green, greenish brown. orangy yellow, brown, grayish black, black. The color is related to the content of Ti and Mn. If there is little of either element, the color is light and may resemble grossular.

Pyrope: purplish red, pinkish red, orangy red, crimson, dark red. Note: Pure pyrope would be colorless; the red colors are derived from Fe + Cr.

Almandine: deep red, brownish red, brownish black, violet red.

Spessartine: red, reddish orange, orange, yellow-brown, reddish brown, blackish brown. Malaya is a pyrope-spessartine from the Umba River Valley of Tanzania; the colors include various shades of orange, red-orange, peach, and pink.

A well-known commercial garnet is intermediate between pyrope and almandine. It is often said that such a garnet is a mixture of “molecules” of these garnets, whereas this really means its structure contains both Fe and Al. The intermediate garnet, known as rhodolite, usually has a distinctive purplish color.

The above variations make it easy to see why it is foolish to try to guess the identity of a garnet on the basis of color alone!

Stone Sizes: Garnet crystals are usually small, microscopic up to about 6 inches in the case of grossular. Garnets in rock, with poor external forms, may be much larger, such as the almandine from Gore Mountain, New York, which reaches a diameter of 60 cm. A few spessartines in Brazil have weighed several pounds and have retained great transparency and fine color, but these are very rare. A typical garnet crystal is about half an inch to an inch in diameter.

Garnets have several species, as well as several varieties. They are listed here, with more detailed information after the general descriptions.

Garnet Species

Pyrope GarnetCHEMISTRY Mg3Al2Si3O12CRYSTALLOGRAPHY Isometric

REFRACTIVE INDEX 1.73 – 1.76

HARDNESS 7 – 7.5

SPECIFIC GRAVITY 3.65- 3.87

DISPERSION 0.022

CLEAVAGE None

HEAT SENSITIVE Some.

DENSITY: 3.65-3.87.

OPTICS: N= 1.730-1.766.

SPECTRAL: The chromium spectrum of emission lines in the far red is absent in pyrope; however, the almandine (iron) spectrum is often visible. Otherwise, Cr masks the almandine spectrum and we see a narrow, weak doublet at 6870/685O, with possible weak lines at 6710 and 6500. A broad band, about 1000 Å wide, may be visible at 5700.

LUMINESCENCE: None.

INCLUSIONS: Pyrope contains small rounded crystals, circular snowballs of quartz crystals, and (from Arizona) octahedra and minute needles.

OCCURRENCE: In peridotites, kimberlites, and serpentine rocks, and sands and gravels derived from their weathering; also in eclogite and other basic igneous rocks.

Utah; New Mexico; Arkansas; North Carolina.

Czechoslovakia; Brazil; Argentina; Tanzania; Transbaikalia, USSR; Bingara, N.S.W, Australia: Anakie, Queensland, Australia; Ottery, Norway.

Arizona: a component of ant hills.

Umba Valley, East Africa: shows color change (see below)

South Africa: in kimberlite and eclogite associated with diamond; fine color

The best known pyrope is from near Trebnitz, Czechoslovakia, the so-called Bohemian garnets. The garnets occur in volcanic breccia and tuffs and conglomerates. These garnets provided a major local industry in the nineteenth Century, but the deposits are exhausted. An enormous quantity of pyrope from these mines was sold.

STONE SIZES: Pyropes of large size are extremely rare. Stones over 1-2 carats are usually very dark. Many large gems are in the Kunsthistorisches Museum in Vienna. There are stories about hen’s-egg-sized gems in the former Imperial Treasury in Vienna. The Green Vaults of Dresden contain a huge gem said to be the size of a pigeon’s egg. Reports of a 468.5 carat gem also appear in the literature.

 

Pyrope

Garnet Jewelry and Gemstone Information

Pyrope comes from a Greek word meaning “fire like.” The common dark red garnets are a mixture of pyrope and almandine.

One popular garnet is chrome pyrope, whose color rivals ruby. These are found in Arizona, where ants bring them to the surface. Hence, they are dubbed, “ant hill garnets.” While their color is superb, they are very dark in tone. Gems are rarely faceted in sizes over one carat because of this.

A pure pyrope (end member in the series) is unknown in nature. Pyropes always contain some almandine and spessartine components. The almandine component can easily be detected spectroscopically. Large, clean pyropes of lively color are very rare and would be very expensive. Some pyropes show an interesting color change. Material from Norway (N= 1.747, S.G. = 3.715) is wine red in incandescent light, violet in daylight, but these stones are very small (about half a carat). Pyrope from the Umba Valley in East Africa (N= 1.757, S.G. = 3.816) are pyrope-spessartines (with some Ca and Ti); they are greenish blue in daylight and magenta in tungsten light. They have inclusions of plates of hematite and rutile needles. All these color-change pyrope-spessartines have absorption bands at 4100, 4210, and 4300 that may merge to form a cutoff at 4350. In stones with a strong change of color, a band at 5730 is broad and strong. Gems sold as pyrope are usually almandines with a pyrope component, especially if they are of large size. The pyropes from South Africa occur with diamonds, and sometimes pyrope crystals are inclusions within diamonds. The color of these is superb, blood red, but the sizes are always very small. Malaya is a variety of Pyrope-spessartine that varies in color from red, through shades of orange and brownish orange to peach and pink. Absorption bands are always visible at 4100,4210, and 4300 that may merge to form a cutoff at 4350. There may also be absorption bands at 4600, 4800, 5040, 5200, and 5370. These stones are only known from Tanzania


Almandine GarnetCHEMISTRY Fe3Al2Si3O12CRYSTALLOGRAPHY Isometric

REFRACTIVE INDEX 1.75 – 1.83

HARDNESS 7 – 7.5

SPECIFIC GRAVITY 3.95- 4.30

DISPERSION 0.024

CLEAVAGE None

HEAT SENSITIVE Some.

DENSITY: 3.95-4.3.

OPTICS: N= 1.75-1.83; usually above 1.78.

SPECTRAL: The spectrum of almandine is distinctive and diagnostic: there is a band 200 Å wide at 5760 (strong) and also strong bands at 5260 and 5050. Lines may appear at 6170 and 4260. This pattern of 3 (or sometimes 5) bands is seen in all almandines, and most garnets with a significant almandine component.

LUMINESCENCE: None.

INCLUSIONS: Almandine is usually included with a variety of minerals. There are zircon crystals with haloes due to radioactivity; irregular, dotlike crystals, and lumpy crystals; futile needles, usually short fibers, crossed at 110° and 70°; there are dense hornblende rods (especially from Sri Lanka); asbestiform needles of augite or hornblende that run parallel to the dodecahedral edges; also apatite; ilmenite; spinet; monazite: biotite; quartz.

Almandine

Garnet Jewelry and Gemstone Information

Almandine is perhaps the commonest garnet. Gemstones always have some spessartine and pyrope components, and this creates a wide range of colors, including brown, red-brown, purplish red, wine red, purple, and deep red. Inclusions of asbestiform minerals (pyroxene or amphibole) create a chatoyancy that yields, in cabochons, a 4-rayed star. Star gems come primarily from Idaho and India. The Idaho material has N= 1.80X, density 4.07 (up to 4.76 due to inclusions). Inclusions in faceted gems vary widely, but are usually not too obtrusive. This is especially true of the silk, which is often visible only under magnification.

One of the classic sources of this garnet is Alabanda, in Asia Minor. Its common name is a modification of the source. The Roman historian Pliny wrote of them.

Almandine is a widespread constituent of metamorphic rocks; also in igneous rocks, in contact metamorphic zones, and as an alluvial mineral.

Colorado; South Dakota; Michigan; New York; Pennsvlvania; Connecticut; Maine.

Canada; Uruguay; Greenland; Norway; Sweden; Austria; Japan; Tanzania; Zambia.

Fort Wrangell, Alaska: fine, well-formed crystals in slate.

California; Idaho: star garnets.

Major gem almandine sources are as follows:

India: Jaipur (in mica schist); also Rajasthan and Hyderabad; some stars also.

Sri Lanka: at Trincomalee, fine color and large size.

Brazil: Minas Cerais; Bahia.

Idaho: star garnets.

Madagascar: large sizes.

Our common, dark red garnets are a blend of almandine and pyrope. Throughout history, this has been one of the most popular gems. They are found world wide and in great abundance. Hence, the value is low.

Very large crystals exist, but because of their dark tone, only small to medium sized gems are faceted. These are cut very shallow, to let light pass through.

Almandine garnets from Idaho and India sometimes have asbestos fiber inclusions. These will produce star stones when properly cut. They are highly prized by collectors, because of their rarity. They are also one of the most difficult gems to cut.

Almandines of large size are known, such as the 60-cm crystals in rock at the Barton Mine, New York. This material is so badly shattered that stones up to only 1-2 carats can be cut from the fragments. Indian and Brazilian almandine constitutes the bulk of material on the marketplace.

Smithsonian Institution (Washington, D.C): 174 and 67.3 (stars, red-brown, Idaho); 40.6 (red-brown, Madagascar).


Spessartite GarnetCHEMISTRY Mn3Al2Si3O12CRYSTALLOGRAPHY Isometric

REFRACTIVE INDEX 1.79 – 1.83

HARDNESS 7 – 7.5

SPECIFIC GRAVITY 3.80- 4.25

DISPERSION 0.027

CLEAVAGE None

HEAT SENSITIVE Some.

DENSITY: 3.8-4.25; gems usually 4.12-4.20.

OPTICS: N= 1.79-1.81;

1.803-1.805 (Brazil).

1.795 (Amelia, Virginia).

SPECTRAL: The Mn spectrum is evident: lines at 4950, 4850, 4620 (all weak) and strong lines at 4320, 4240 (weaker), and 4120 (intense). Almandine may be present, contributing lines at 4320 and 4120.

LUMINSCENCE: None.

INCLUSIONS: Wavy feathers, due to liquid drops that have a shredded look, especially in gems from Sri Lanka and Brazil.

Spessartite

Garnet Jewelry and Gemstone Information

This garnet is named after Spessart, Bavaria.

Spessartite is somewhat rare. As with the other garnets, it always occurs in a blend with other species. Gems with the highest spessartite content are a light orange. Those with an almandine content are reddish, to red brown in hue.

In granite pegmatites; also gneiss, quartzite and rhyolite, and sometimes as a component in skarns.

Nevada; Colorado; New Mexico; Pennsvlvania; North Carolina.

San Diego County, California: good crystals, especially at Ramona (fine orange gems).

Amelia Court House, Virginia: fine orange to deep brownish material, gemmy.

Norway; Tsializina. Madagascar

Sri Lanka and Burma: in the gem gravels.

Brazil (Arassuahy and Ceara): large crystals (up to several pounds), gemmy, fine color.

The most valuable spessarties are a bright, orangish red. These come from Ramona, California, and Amelia, Virginia..

Gems weighing more than 100 carats have been cut from Brazilian and Madagascar rough. Amelia stones are fine color (orange) but small, up to about 15-20 carats, although crystals weighing several pounds have been found there.

Smithsonian Institution (Washington, D.C): 109 (red, Brazil); 53.8 (red, Brazil); 40.1 (orange, Virginia). American Museum of Natural History (New York): 96 (reddish, Brazil—not clean).

Spessartine is fairly rare as a gem garnet, and one of the most beautiful. Large stones are very rare, and usually quite dark. The finest color is an orangy red, as exemplified by the material from Ramona, California, and Amelia, Virginia. A red-brown tint indicates a higher content of almandine, accompanied by higher refractive index; pale orange colors are closer to pure spessartine. Spessartine as a component of almandine tends to add a lively reddish tinge of color.

Spessartine is fairly rare as a gem garnet, and one of the most beautiful. Large stones are very rare, and usually quite dark. The finest color is an orangy red, as exemplified by the material from Ramona, California, and Amelia, Virginia. A red-brown tint indicates a higher content of almandine, accompanied by higher refractive index; pale orange colors are closer to pure spessartine. Spessartine as a component of almandine tends to add a lively reddish tinge of color.

Unusual color-change garnets with large amounts of V and Cr have been reported from East Africa. These are primarily spessartine, with an unusually large component of grossular. The color change may be as follows: 1. greenish yellow-brown (transmitted fluorescent light) to purplish red (reflected fluorescent); reddish orange to red (incandescent light) N= 1.773, S.G.= 3.98; spessartine/grossular/almandine.

2. light bluish green (transmitted fluorescent) to purple (reflected); light red to purplish red (incandescent) N= 1.763, S.G. = 3.89; spessartine/grossular/pyrope.

So-called alexandritelike garnets have also been noted, changing from violet-red to blue-green. These are usually small, but a stone of 24.87 carats was sold in 1979.


Andradite GarnetCHEMISTRY Ca3Fe2Si3O12CRYSTALLOGRAPHY Isometric

REFRACTIVE INDEX 1.86 – 1.95

HARDNESS 6.5 – 7

SPECIFIC GRAVITY 3.70- 4.10

DISPERSION 0.057

CLEAVAGE None

HEAT SENSITIVE Some.

DENSITY: 3.7-4.1; melanite about 3.9; demantoid 3.82-3.88.

OPTICS: N= 1.88-1.94; melanite:  1.89; demantoid: 1.881-1.888; schorlomite: 1.935; topazolite (yellow): 1.887.

SPECTRAL: A strong band is visible at 4430, cutoff at the violet end of the spectrum. Sometimes (in demantoids) the Cr spectrum is visible, with a doublet at 7010, sharp line at 6930, and 2 bands in the orange at 6400 and 6220. Demantoid is red in the Chelsea filter.

LUMINESCENCE: None.

INCLUSIONS: Demantoid is distinguished by so-called horsetail inclusions of byssolite (fibrous amphibole); these are diagnostic for this gem. These inclusions also occasionally produce catseye gems.

Andradite

Garnet Jewelry and Gemstone Information

Andradite is named after the Portuguese mineralogist, d’Andrade.

Melanite has 1-5% Ti oxide; schorlomite is rich in Ti also; topazolite from Italy is yellowish-green; demantoid is rich green, colored by Cr.

This is one of the rarest and most sought after garnets. There are no major sources of andradite and the supply is limited to small deposits.

Andradite occurs in schists and serpentine rocks (demantoid and topazolite); also in alkali-rich igneous rocks (melanite and schorlomite); and in metamorphosed limestones and contact zones (brown and green colors).

San Benito County, California: topazolite (N= 1.855-1.877, S.G. = 3.77-3.81), demantoid (N= 1.882, S.G. = 3.81), and unusual catseye material. Arizona: New Jersey; Pennsylvania.

Greenland; Norway; Sweden; Uganda; Ski Lanka. Colorado: melanite.

Arkansas: schorlomite.

New Mexico: in metamorphic limestones and ore deposits.

USSR: fine demantoid from the Urals. Also some (small) brown andradite.

Zaire: brown and green andradite, also some demantoid.

Ala, Piedmont, Italy: dark apple green demantoid garnet; also topazolite (yellow).

Korea: andradite, some fine green with Cr.

Monte Somma, Vesuvius, and Trentino, Italy: melanite (black).

Its dispersion is much higher than any other garnet and even much higher than diamond. The dispersion is usually masked by dark body colors but small, light colored gems are dazzling!

The variety dematoid is colored green by chromium. This gem is always in high demand.

Andradites are known for their distinctive, horsetail inclusions. (See “Identifying Inclusions” in our Reference Library.) They are both an aid to the gemologist and a delight to collectors.

Andradite is seldom faceted, but brownish stones up to a few carats are known. Demantoid however, is a rare but well-known gem, and is probably the most valuable of all the garnets.

Smithsonian Institution (Washington, D.C): 10.4 (USSR); also 4.1, 3.4, and 2.3.

Private Collection: 18 (sold in New York Cityl; a California collector owns a huge topazolite (green color) that would yield faceted gems over 20 carats. This crystal weighs ~1 ounce.

USSR: many fine demantoids in museum collections.


Grossular GarnetCHEMISTRY Ca3Al2Si3O12CRYSTALLOGRAPHY Isometric

REFRACTIVE INDEX 1.72 – 1.80

HARDNESS 6.5 – 7.5

SPECIFIC GRAVITY 3.40- 3.70

DISPERSION 0.028

CLEAVAGE None

HEAT SENSITIVE Some.

DENSITY:  3.4-3.71; usually near 3.65.

OPTICS: N= 1.72-1.80; usually 1.73-1.76 (with V= 1.743-1.759).

SPECTRAL: None in pale-colored, faceted gems; a trace of almandine may produce a faint iron spectrum. A trace of Cr may produce a chrome spectrum in green varieties. Massive grossular may show a weak line at 4610 or a band at 6300. Green, massive grossular from Pakistan shows a line at 6970 (weak) with weak lines in the orange, plus a strong band at 6300 and diffuse lines at 6050 and 5050. Orange stones may have bands at 4070 and 4030.

LUMINESCENCE: Usually none in UV. All massive material glows orange in X-rays, as do many faceted gems.

Grossularite

Garnet Jewelry and Gemstone Information

Also known as hessonite, essonite, cinnamon stone; rosolite is a pinkish variety from Mexico.

The botanical name for gooseberry is grossularia, from which this garnet receives its name.

Unlike the other garnets, grossulars are rarely red or dark. They come in every color except blue and are sometimes colorless. The tone is often light to medium. They make brilliant gems with vibrant colors.

In metamorphosed, impure calcareous rocks, especially contact zones; also in schists and serpentines; worldwide occurrence, widespread.

Eden Mills. Vermont: fine orange crystals, some gemmy, with green diopside.

California: many localities.

New England: many localities.

Asbestos, Quebec, Canada: fine orange to pinkish crystals at the Jeffrey Mine, up to 2 inches across, gemmy.

Also colorless (N= 1.733).

Lake Jaco, Chihuahua, Mexico: large pinkish, white, and greenish crystals: color zoned concentrically, usually opaque; crystals up to about 5 inches in diameter.

Sri Lanka: grossulars are found in the gem gravels (hessonite).

Wilui River, USSR: opaque green crystals with idocrase.

China: massive white grossular.

Australia (Harts Range. Northern Territory): hessonite.

New Zealand: hydrogrossular.

Kenya and Tanzania: fine grossular in various colors, especially the dark green material being marketed as tsavorite, containing V and Cr.

South Africa: massive green material that resembles jade.

Pakistan: some faceted green gems: also massive green grossular, various shades.

Brazil; Switzerland.

Hydrogrossular and massive varieties are cut as cabochons of large size, including green shades and also pink, translucent grossular. Massive white material from China has been carved. Orange and brown grossulars up to several hundred carats from the Sri Lankan gem gravels have been found; the fine cinnamon colored stones from Quebec are clean only in small sizes, but good gems up to about 25 carats have been cut. Tsavorite is rare in clean gems over I carat: the largest known are in the 10-20 carat range.

Smithsonian Institution (Washington, D.C): 64.2 (orange-brown, Sri Lanka)

Private Collection: 13.89 (yellow, oval).

American Museum of Natural History (New York): 61.5 (cameo head of Christ, hessonite).

NMC: 23.94,13.40,8.50 (brownish-orange hessonite, Asbestos, Quebec); 4.68, 2.94 (colorless, Asbestos, Quebec).

Grossular has a granular appearance under the microscope, sometimes referred to as treacle, a swirled look due to included diopside crystals and irregular streaks at grain boundaries. Zircon crystals are included in some grossulars. as well as actinolite and apatite (Tanzania material). So-called Transvaal jade is the green massive matenal from South Africa. The color of grossular depends on the content of Fe and Mn. If there is less than 2% Fe, grossular is pale or colorless. Greater amounts of Fe produce brown and green colors, and a rich green shade is due to Cr. Californite is a mixture of idocrase and grossular, usually pale to medium green in color. It comes from California, Pakistan, and South Africa.

Hydrogrossular is a component of the massive grossulars. Material from New Zealand is known as rodingite (N= 1.702, density 3.35). Transvaal jade occurs in green, graygreen. bluish, and pink colors, is compact and homogeneous, may have a splintery fracture and waxy luster. The gray material contains zoisite. Pink material, containing Mn, has N= 1.675-1.705, density 3.27. The green, jadelike material has N= 1.728, density 3.488. Pakistan massive grossular has N= 1.738-1.742, density 3.63, with a Cr absorption spectrum. Similar material from Tanzania has N= 1.742-1.744, density 3.68.

Colorless grossular from Georgetown, California, has

N = 1.737, density 3.506. Yellow garnet from Tanzania fluoresces orange in X-rays and also UV, N= 1.734, density 3.604. Tsavorite from Lualenyi, Kenya, has N= 1.743, density = 3.61 (mean). It is inert in UV light, contains a trace of Cr and a significant amount of vanadium. The color of these tsavorites is therefore due to vanadium, not chromium as originally suspected.

The pinkish grossular in marble from Lake Jaco and Morelos, Mexico, is variously known as xalostocite, landerite, and rosolite.


Hydrogrossular GarnetCHEMISTRY Ca3Al2(SiO4)3-x(OH)4
CRYSTALLOGRAPHY Isometric
REFRACTIVE INDEX 1.72 – 1.80
HARDNESS 6.5 – 7.5
SPECIFIC GRAVITY 3.40- 3.70
DISPERSION 0.028
CLEAVAGE None
HEAT SENSITIVE Some.

Hydrogrossular

Garnet Jewelry and Gemstone Information

Hydrogrossular differs from the other garnets in that it is never transparent. It ranges from translucent to opaque. The most common color is a bluish green, but they are also found in pink, white, and gray.

Because of its coloring and translucency, hydrogrossular is often used as a jade substitute. Large pieces are available, which lend themselves to carving..


Uvarovite GarnetCHEMISTRY Ca3Cr2Si3O12CRYSTALLOGRAPHY Isometric

REFRACTIVE INDEX 1.74 – 1.87

HARDNESS 6.5 – 7.5

SPECIFIC GRAVITY 3.40- 3.80

DISPERSION unknown

CLEAVAGE None

HEAT SENSITIVE Some.

DENSITY:  3.4-3.8 (usually 3.71-3.77).

OPTICS: N= 1.74-1.87.

Uvarovite

Garnet Jewelry and Gemstone Information

Uvarovite is named after Count S. S. Uvarov, (1765-1855), president of the St. Petersburg Academy and mineral collector.

This is the rarest of the garnet family. Colored by chromium, it is always a dark, rich green. The crystals are small and most people have only seen examples of druzy on matrix.

Faceted uvarovites are extremely rare because crystals are always opaque. An occasional crystal may have a transparent corner that could yield a stone of less than 1 carat, even though crystals may reach a size of 1-2 inches.

The crystals are usually opaque. Only small corners of larger crystals have the transparency for faceting. Anything over one carat is exceptionally rare for a faceted uvarovite. Collectors are grateful to have a faceted uvarovite of any size. They are so rare; there simply are not enough to go around.

The color of uvarovite is like that of emerald (deep, rich green), so it is a shame that crystals cannot be cut. Uvarovite is a rare mineral, prized by collectors. It is not generally regarded as a gem garnet.

 

Garnet Varieties


Garnet Jewelry and Gemstone Information

Rhodolite

Rhodolite is intermediate in composition between almandine and pyrope, with a ratio of Al to Fe of 2 to 1 (that is, 2 pyrope + 1 almandine). The distinctiveness of rhodolite is in its color, which is nearly always a purplish red.

The absorption spectrum always shows almandine lines Inclusions include apatite crystals (North Carolina) and any of the other inclusions found in almandine. The color of a garnet is misleading, and a chemical analysis is

required to show whether a garnet is an almandine or pyrope, or a mixed crystal.

Density:  3.79-3.80 (Tanzania); 3.83-3.89 (Zimbabwe); 3.84-3.89 (North Carolina).

Optics: N= 1.750-1.760 (Zimbabwe);

1.760-1.761 (North Carolina);

1.745-1.760 (Tanzania).

Dispersion: 0.026.

Occurrence: North Carolina: rhododendron red. lilac, pinkish.

Sri Lanka; Madagascar; India; Tanzania; Zimbabwe.

Stone Sizes:

Smithsonian Institution (Washington, D.C): 74.3, 22.1 (Tanzania); 16.5 (North Carolina).

Comments: The original locality for rhodolite was Cowee Creek, Macon County, North Carolina. Stones from this locality are usually very small (under 1-2 carats), but new finds in Africa have yielded gems over 75 carats. Material from the North Pare Mountains, Tanzania, may show a color change, blue in daylight to purplish red in incandescent light, similar to alexandrite (N= 1.765, S.G. = 3.88).

Some say the name rhodolite comes from the Greek word, rhodon, meaning rose. Other scholars compare the name to rhododendron. In either case, the name is comparing the color to a flower.


Garnet Jewelry and Gemstone Information

Malaia

Malaia is a Bantu word that means out of the family, or out of the tribe. It is also used to mean prostitute or deceiver. It came into usage for a number of garnets that did not fit into any of the standard categories.


Garnet Jewelry and Gemstone Information

Dematoid

Dematoid comes from the French, “demant,” meaning diamond. The reason is obvious, with its high brilliance and dispersion. Dematoid garnets are a green variety of andradite. They are known for their golden, “horsetail” inclusions.


Garnet Jewelry and Gemstone Information

Tsavorite

Tsavorite is named after its only source, the Tsavo Valley in Kenya. It is the chromium colored, green variety of grossular.

These popular gems demand high value in today’s market. While faceted stones approaching 20 carats are known, their deep coloring usually keeps their size below three carats.


Garnet Jewelry and Gemstone Information

Hessonite

Hessonite is from a Greek word meaning inferior. This refers to it having less hardness than other garnets.

Hessonites are an orangish variety of grossular garnet. Sometimes their coloring leans towards the pink. Asbestos, Quebec is one of the most common sources. The miners find pinkish orange crystals among the asbestos. Africa is also a major source for hessonite.


Color Change Garnets

Garnet Jewelry and Gemstone Information

Any gem that changes color is a rare find and a treat for collectors. Garnets exhibit the widest variety of color changes in the gem world, with almost every hue exhibited.

It is commonly said that garnets come in every color of the rainbow except blue. This is still true in natural light, but there are recent discoveries of garnets that turn blue in artificial light.

Color change garnets are mostly pyrope and spessartite in composition. Except for the color change, they are identical in properties to the Malaia variety. Their primary source is Africa.

Idaho garnets, which are primarily almandine/pyrope mixtures, occasionally show a strong color shift from red to purplish red.


Proteus

Garnet Jewelry and Gemstone Information

In Greek mythology, Proteus was a sea god, capable of changing his shape. It has become a noun for one who easily changes their appearance or principles.

Proteus are the only treated garnets. All the others resist change, but a few almandine/pyropes from the US will change into Proteus. The treatment brings a thin layer of metals to the surface.

This causes it to have a dual appearance. In reflected light, they have a dark gray, metallic luster, much like hematite. In transmitted light, the dark red of the garnet shows through.

SOURCES:

Garnet Jewelry and Gemstone Information

Dr. Joel Arem

The IGS gratefully acknowledges Dr. Joel Arem for generously allowing us to utilize his content above with attribution.

 

See related articles by category: Gem Listings, Reference Library

Products and Services Directory

Looking for gemology related products and services? Visit our Products and Services Directory.

Scholarships

IGS seeks to encourage the advancement of students pursuing a higher education. Learn more about the 2014 Clark Scholarship.

eNews Signup

Membership Login