Sphalerite Buying Guide
Sphalerite offers a great temptation for jewelry lovers. Faceting and polishing can enhance this gem’s high dispersion or fire and take its luster to a bright, diamond-like adamantine. Rough gem material in rich green, yellow, orange, brown, and red colors isn’t hard to find.
However, for all its beauty, this gem is too soft and fragile for most jewelry uses. It has six perfect cleavage planes in its isometric crystal structure, it’s brittle, and scratches easily. (Sphalerite has a hardness of 4. Common household dust, with a hardness of 7, would scratch sphalerite if you wiped it off with a cloth). Faceting this soft, often color zoned, highly cleavable gem presents a challenge few faceters can meet successfully.
As a result, you’ll find relatively few cut specimens, even though rough is available. If this material were tougher, it would probably be a very popular, important gem. As it stands, you have a chance to add a breathtaking faceted specimen to your gem collection or an unusual, special occasion piece to your jewelry collection.
Sphalerite Buying and the 4 Cs
The IGS sphalerite value listing has price guidelines for faceted pieces.
Color
You’ll find that fine red or orange sphalerites, especially in sizes above 3 carats, command high-end prices. Generally, green, yellow-green, and brownish stones have lower values, as do smaller pieces of any color.
Colored gems with lighter tones typically display their dispersion to greater effect than darker stones. However, sphalerite has a refractive index (RI) that can range somewhat higher than diamond’s. Its dispersion also exceeds diamond’s famously high value over three times. That means, a well-cut and polished sphalerite can show multicolored light flashes, even when seen against a richer body color. (Since colorless and pale sphalerites are much rarer than darker specimens, this is great for fire enthusiasts).
Clarity
Clarity refers to a gem’s transparency and anything that can impact how it transmits light.
Eye clean or better faceted sphalerites are preferable. However, with cut material so scare, buyers will usually tolerate some inclusions if the stone’s other qualities are good.
Larger stones (over 20 carats) usually have some inclusions, as well as veils and flaws. Completely transparent sphalerites are considered rare.
Cut
For sphalerites, cutting is all-important, since these gems are difficult to cut well. In addition, the quality of the surface polish greatly affects the appearance of a cut gem. Cuts that emphasize brilliance, standard rounds and squares as well as fancy cuts like trillions and cushions, can work well. (Expert gem cutters will balance brilliance and color when dealing with darker colored sphalerites).
Editor’s Note: For sphalerites, Jeff Graham generally recommends gem designs suitable for zircons. Search his gemstone faceting diagrams for more specific zircon/sphalerite friendly designs.
Carat
Sphalerites have no significant jumps in price per carat.
Jewelry Considerations When Sphalerite Buying
Adventurous jewelry buyers as well as jewelers may wish to set these lovely stones. If worn carefully and only on special occasions, a pendant or brooch may be an option. Ring use is not advisable. Overall, these gems are better suited to gem collections than jewelry collections.
Sphalerite is heat sensitive, fragile, and brittle. These qualities rule out using mechanical cleaning systems such as ultrasound, steaming, or boiling. Clean these gems only with a soft brush, mild detergent, and warm water.
Synthetic sphalerites do exist. These gems still share the natural gem’s low hardness and fragility. However, they can be created in any of the gem’s natural colors, including the rarer colorless and pale shades. A gemological laboratory may be able to distinguish a synthetic from a natural gem.
You might encounter other gems, both natural and synthetic, as sphalerite simulants. Natural zincite is rare, but synthetic zincite is common and may be presented as sphalerite, despite notable differences, including birefringence. On the other hand, cassiterite, a high dispersion gem, also occurs in yellow, brown, green, and red colors, like sphalerite. However, it’s harder, easier to facet, and rarer. You might find sphalerites misidentified as cassiterites.
Best Sources for Sphalerite Buying
Spain produces wonderful, gem-quality yellow, orange, and red specimens. Mexico produces gem-quality greenish and brownish stones. Franklin, New Jersey yields the very rare, pale to colorless facetable variety of sphalerite.
