Published: February 2012
George Williams & Jerry Sisk, JTV®
A rare treasure for gemstone collectors, sphalerite (pronounced SFAY-luh-ryte) has a fire and brilliance that is unforgettable. With a greater rate of dispersion than that of a diamond, sphalerite is said to have an adamantine, or "diamond like", luster.
Known primarily to collectors due to its lack of hardness (3.5-4 on the Mohs scale), sphalerite can be a challenging material to fashion into gems. Not only is it extremely soft, it also has perfect cleavage--in six directions, making it even difficult to cut and polish. Add in the fact that it's a brittle gem, and you can see the challenge awaiting lapidaries. Yet, when a talented lapidary is able to complete his task with a fashioned gem, the results are spectacular.
This gemstone is named from the Greek sphaleros, meaning treacherous. Because sphalerite resembles several minerals in appearance, including galena, it presents difficulty to miners when trying to identify it in the field.
Mother Nature wasn’t shy as she was mixing sphalerite’s formula--it is a zinc oxide that contains varying amounts of iron. Crystal formation varies and twinned crystals are common. Found in a variety of forms, sphalerite is often called zinc blende, as it is a major worldwide source of zinc ore.
Sphalerite colors include a full spectrum from yellow to red and it’s often seen in various shades from yellow to green, and ending in black. As the iron content of the gemstone increases, the stones become darker. Red to brownish red crystals are sometimes called ruby zinc, or ruby blende, and black crystals are called black jacks. Depending on its origin, some sphalerite may fluoresce from orange to red under ultraviolet light.
Additionally, sphalerite has a couple of interesting properties. It is both pyroelectric (becomes electrically charged when heated) and triboluminescent (begins to glow when rubbed, pressed or struck). Sphalerite’s luster varies quite a bit, depending on its crystal habit and chemical nature. With a gem quality specimen, you can rotate it and see a magnitude of bright flashes, with hundreds of sparkling facets.
While sphalerite is found in several locations worldwide, only a few locales provide material that is gem quality. Spain and Mexico are the two most notable sources for fine quality material, while lesser deposits are found in Canada, Germany and the United States.