Sphene is highly regarded as a gemstone by collectors, but scarcity has kept it out of the commercial market until now. The discovery of new deposits should ensure that this brilliant little gem finally achieves the attention it deserves.
Gem-quality sphene comes in a range of clear bright tones: grass green, golden yellow, brownish yellow and reddish brown. The most sought-after and expensive colour is chrome green, and there are also bicoloured stones in a mix of green and orange-brown. Sphene is strongly pleochroic, showing three different colours when viewed from different angles: colourless, greenish yellow and reddish. It is a wonderfully brilliant gemstone that possesses an adamantine lustre and a dispersion that is greater than that of a diamond. Under incandescent light the brilliance is amplified.
Sphene has a high birefringence (double refraction), which results in the doubling of the back facets. “Clean” rough material is difficult to find and it is very rare to get a clean stone over 10 carats, but faceted stones are still stunning, even with minor inclusions, due to the remarkable properties of the material. A gemstone will usually contain needlelike and rounded plagioclase inclusions, as well as veils and mistlike inclusions.
Treatments and imitations
– Sphene is often heat treated to change the colour to red or orange tones.
– It could be confused with chrysoberyl, dravite (golden brown tourmaline), heliodor, topaz or zircon (which also has a high dispersion).
The availability of sphene can fluctuate slightly, but it is easy enough to get clean stones up to 2 carats in weight. The material is moderately priced at this size, but larger stones over 3 carats are harder to find and more expensive. Sphene is not available in bead form.
Working with sphene
– Sphene is a moderately soft gemstone, but would be suitable for pendants or earrings. If it were to be used for a ring it would need to be protected and kept for occasional wear only. Do not use ultrasonic cleaners and take care during polishing. Treat sphene as you would an opal.
– Cutting sphene is a considerable challenge. The material has perfect cleavage and a conchoidal, brittle fracture, which means that it chips easily. The pleochroism and high birefringence have to be taken into account when orienting the table for faceting; the best colour should be seen from the top through the table and there should be no blurring of the back facets. Round and oval brilliant cuts are more suitable for sphene as they are less likely to result in damage or chipping. The brilliant cut was designed for a gem with high dispersion, so it will make the most of sphene’s brilliance and fire. Princess cuts and baguettes are not suitable.