Distinguishing Features
Historical Gems: A stylish red garnet bead necklace found in a grave in Egypt is more than 5,000 years old.
More than twenty garnet species exist, but only a few are commercially important as gems. Many garnets are mixtures of two or more garnet species.
The illustration below shows how gemologists divide garnets according to their chemistry, optical and physical properties to help with identification. However, many dealers sell garnets based on colour or origins.
The Most Desirable Picks
Green Garnets:
Tsavorit’s best colour is pure green or green with a slight blue. Large tsavorite rough is extremely rare.
Demandoits most desirable colour is a moderately strong to strongly saturated green of medium to medium-dark tone. It has a vivid green colour and higher dispersion than diamond.
Orange Garnets:
The favourite colour of Spessartine garnet is a vivid “Aurora red”, which is a highly saturated, slightly reddish-orange hue with a medium to medium-dark tone.
Malaya, a pinkish to reddish-orange garnet, stood out from the purplish-red rhodolite when people were mining in Tanzania’s Umba River Valley.
Hessonite is the transparent orange to a cinnamon-coloured variety of the grossular species. Still, it almost always has a brownish hue and is too included to be used in jewellery.
Red Garnet
The most valuable red garnet rhodolite has a dark purplish-red to light reddish-purple hue. The bests have medium to medium-dark tones, strong saturation, good brilliance and little extinction.
Pyrope and almandine combine to form rhodolite and other red garnet varieties. Both appear in a range of orange-red to slightly purplish red to strongly reddish-purple hues. They exist as separate species as well. The best stones of pyrope garnets are a highly desirable intense pure red, like a ruby.
Vast numbers of dark-toned, reddish-brown, calibrated pyrope-almandine garnets are used in inexpensive, massive market jewellery. “Mozambique” and “African” are terms widely used in the trade.
Phenomenal Garnets:
Colour-change garnets from Africa and Sri Lanka are strongly red under one light source and green or even blue under another. The most striking examples have blue to bluish-green hue in daylight or fluorescent light and purple to purple-red in incandescent light.
Star garnets are found in India, Sri Lanka and Idaho, US. They are filled with silk needles that cause asterism, usually almandine or rhodolite.
Clarity:
Typical garnet clarity depends on the garnet type. For example, the red garnets usually do not have eye-visible inclusions. Some of the orange garnets often have eye-visible inclusions.
Cut:
Many garnets are cut into calibrated shapes and sizes to set into jewellery easily. However, expensive roughs deserve case by case design. Garnets like fine-quality tsavorite are cut into shapes and cutting styles that would retain more weight from the rough.
Carat Weight:
Garnets range in all sizes and weights. Some garnets are rarer in large sizes, such as demantoid and tsavorites; thus, their prices go up considerably with size. Other garnets, such as almandine, are far more common in larger sizes and are less sensitive to size differences.
Origins
Green Garnets:
Tsavorite is mined chiefly in East African countries of Tanzania, Kenya, and Madagascar, although there are some minor sources in Pakistan.
Demantoid comes primarily from sources in Russia and Africa. Inconsistent supply and continuing demand are keeping the prices high.
Orange Garnets:
Spessartine was first discovered in Bavaria, Germany. Like the Little Three mines in Ramana, California, the Rutherford mines in Virginia, some other mines have never been the big producers. Discoveries of spessartine in the 1990s made it much more available. New deposits in Madagascar, Namibia, Tanzania, Zambia, India, Pakistan, Sri Lanka, Brazil and especially Nigeria helped increase the supply.
Red Garnets:
Rhodolite was first discovered in the state of North Carolina, US. East Africa has been the most important source in recent years. Other significant sources today include Sri Lanka, India’s Orissa state and Madagascar.
Significant Pieces
This antique hair comb was donated in 1937 by Ales & Maria Herdlicka. It has Bohemian pyrope garnets from the Czech Republic, historically the principal source of these red garnets that were popular in Victorian jewelry (1837-1901). Garnets were often mounted in yellow gold, gold plate and mixed metal settings during this time. Bohemian garnet jewelry is known for its encrusted close-set stones which are often rose cut (faceted top and flat bottom, as seen here) and are sometimes combined with other larger faceted stones or cabochons. Pyrope gems are the reddest of all garnets, typically very dark red to slightly brownish-red and seldom are larger than a few carats. Pyrope has been confused with ruby, due to its fiery red color, and derives its name from the Greek pyropos, meaning “firelike.” Until the late 19th century, Bohemia was the main source of pyrope garnets. However, limited availability today precludes widespread use in modern jewelry.
Description Courtesy: Smithsonian National Museum of Natural History
Formation
Many garnets are mixtures of two or more garnet species. The mixtures are possible because chemical elements can substitute for one another in a mineral’s crystal structure. The substitution of a chemical component for another in a mineral’s crystal structure is an isomorphous replacement.
For example, Phyrope and almadine have identical crystal structures. In addition to the essential elements in silicon, oxygen, and aluminium, almandine contains iron and pyrope contains magnesium. Iron and magnesium can substitute for each other, they can mix. In nature, no garnet is ever pure. Garnet species mix to produce a range of gems with different colours and physical properties.