Radiant square-cut sphalerite, 198 cts, 30.1 x 30.3 x 21.1 mm, Las Manforas, Aliva, Picos de Europa, Spain.
Does Sphalerite Make a Good Jewelry Stone?
Sphalerites have low hardness (3.5 to 4) and perfect cleavage, which make them less than ideal as jewelry stones. Nevertheless, sphalerites can show beautiful colors and may appeal to collectors of unusual gems. Use protective settings for these gems, especially if worn as ring stones.
This 18K gold cocktail ring setting allows light to enter the 35.7-ct sphalerite center stone but still protects it from scratches and blows. The ring also features pavé diamonds and tiny sphalerites. Photo courtesy of liveauctioneers.com and I.M. Chait Gallery/Auctioneers.
For custom cutting, you can easily find facetable sphalerite rough in most colors. Faceting this material, however, poses a challenge. Consult our sphalerite buying guide for more information.
What Color is Sphalerite?
Sphalerites come in many colors, including brown, orange, yellow, green, orange-red, red, whitish gray, black, and even (very rarely) colorless. Sphalerites can also show color zoning.
According to a 1984 study by Hoffmann and Henn, a number of trace elements may contribute to color in sphalerites. These include germanium, calcium, copper, mercury, and cerium (yellow); tin, silver, and molybdenum (reddish); and cobalt and iron (green). (p. 49) Iron-rich sphalerites appear black.
Sphalerite Names and Varieties
Iron-rich, opaque, black stones are known as marmatites, named after the locality, Marmato, Italy.
In Europe, sphalerite is sometimes called blende, after the German word blenden, “to dazzle.” Though they have no connection to actual ruby gems, stones with red and orange shades are sometimes called “ruby blende.”
Low-iron, pale and colorless sphalerites, known as cleiophanes, are extremely rare.
Identifying Sphalerites
Sphalerites have an exceptionally high dispersion of 0.156. Well-cut sphalerites can display a beautiful rainbow effect of multi-colored flashes of light. Only other rarely faceted gemstones have comparable dispersion values. Gemologists can measure a gem’s dispersion using a refractometer or a spectrometer. However, keep in mind that cut quality, color, and specific gravity can affect how well a specimen displays dispersion.
Sphalerite and wurtzite are polymorphs. They share the same chemical formula (ZnS), but have different crystal habits. Sphalerite has an isometric crystal structure, while wurtzite has a hexagonal structure. These two minerals can coexist in alternating layers as schalenblende, a gem material used rarely for cabochons.
Sphalerites may have a streak color ranging from pale brown to yellow or white. Keep in mind that streak testing can destroy the test sample. Conduct this examination only as a last resort for gem identification on rough, never on a finished gem. This test will also release a sulfurous odor from the test sample.
Sphalerites are pyroelectric. When heated, these gems generate an electrical charge.
Sphalerites may show anomalous double refraction due to crystal strain.
Refractive index and specific gravity in sphalerites may vary due to variable chemical composition.
Are There Synthetic Sphalerites?
Since sphalerite ranks as the primary ore for zinc mining, scientists have synthesized this mineral for industrial research. In addition, facetable synthetic sphalerites in all their colors have appeared in jewelry and gem collections.
There are no known gemstone treatments for sphalerites.
Are There Cat’s Eye Sphalerites?
Sphalerites don’t normally display cat’s eye or star stone effects. However, in a 2009 study, researchers Hyršl and Steinbach found that polishing scratches on the bottoms of sphalerite cabochons may cause apparent chatoyancy and asterism. In this case, these scratches may have occurred accidentally. (pp. 303-304)
Where are Sphalerites Found?
Significant gem-quality sources include the following:
- Santander, Spain: major gem locality, large cleavages of red-orange color.
- Cananea, Sonora, Mexico: fine green transparent material, often pale colored and color zoned, sometimes yellow.
- Kipushi, Democratic Republic of the Congo: dark green material containing elevated amounts of cobalt and iron.
- United States: Franklin, New Jersey (almost colorless to pale green, transparent variety known as cleiophane); Kansas/Missouri/Oklahoma (so-called Tri-State Region, heavily mineralized by lead and zinc, with many localities and operating mines); Tiffin, Ohio (red color); Colorado/Utah (may be transparent); Arizona; Idaho; Montana; Wisconsin.
- Australia; Bulgaria; Canada; China; Czech Republic; England; France; Germany; Tsumeb, Namibia; Romania; Scotland; Sweden
Sphalerite Stone Sizes
From the large, reddish material from Spain, faceters could easily cut gems of hundreds of carats, as well as cabochons. Green cleiophane material from New Jersey has yielded faceted gems as large as 15 carats. Mexican material could yield faceted gems to 50 carats.
- Smithsonian Institution (Washington, DC): 73.3, 68.9 (yellow-brown. Utah); 59.5 (yellow-green, New Jersey): 48 (yellow, Mexico); 61.9, 45.9 (yellow, Spain).
- California Academy of Sciences (San Francisco): 150.3 (dark red-brown oval, Spain).
- National Museums of Canada (Ottawa, Ontario): 100.1 (dark orange, round, Spain).
- Private Collection: 24.8 (gray-green, Mt. Ste. Hilaire, Quebec).
How to Care for Sphalerite Jewelry
Clean sphalerites only with a soft brush, mild detergent, and warm water. See our gemstone jewelry cleaning guide for more recommendations.
Works Cited
Hoffmann, C. and U. Henn, reviewed by Mahinda Gunawardene. “Grüne Sphalerite aus Zaire (Green sphalerite from Zaire).” Gemological Abstracts. Gems & Gemology, Spring 1985. (Accessed 4/25/24)
Hyršl, Jaroslav and Martin P. Steinbach. “Pseudo-chatoyancy and pseudo-asterism in sphalerite from Spain.” Gems & Gemology, Winter 2009. (Accessed 4/25/24)
