Sphalerite is a little-known gemstone. It’s relatively soft at 3.5-4 on the Mohs scale, but it has a very high refractive index (2.368 to 2.371) and very high dispersion or “fire;” much more so than diamond. It has an adamantine to sub-metallic luster. The combined effect is impossible to capture in a photo, but it gives this gemstone an amazing brilliance and fire that immediately catches the eye. Large clean pieces of sphalerite are not common, and its challenging to facet and polish into a gemstone, so its not often seen for sale.
This particular gem comes from a parcel of rough I acquired from a mine in Spain. I faceted it in my custom “Helena” brilliant oval design, and the resulting gemstone is incredibly bright in the hand; the dispersion has to be seen in person to be fully appreciated. The tiny inclusions visible in the macro photos are not visible in the hand–its eye clean. The gem weighs 1.83 carats and measures 7.3 x 6.2 x 4.9 mm.