The Aliva sphalerite’s colors range from black to brown, yellow, green, orange, and intense red (called in the gemological field “ruby blende”). The most typical sphalerites have toffee color, known in Spain as "blenda acaramelada" (toffee-blende).
In larger crystals, rear illumination is needed to appreciate their real color. Otherwise they seem to be dark or black. However, with the appropriate illumination they either reveal to be translucent and be orange, toffee, red or black and opaque due to multiple inclusions in low quality crystals.
Their color can range from rare to more common: colorless, green, and red are very rare, while brown, orange and yellow are common. Moreover, sphalerites with highly saturated colors are more common than the stones with low saturation color, contrary to the majority of colored gemstones. Clear colored sphalerites are highly prized and very difficult to find, especially the large stones with good clarity, which will display the greatest dispersion.
Typical colors of Spanish gem sphalerites are represented below, with some comments on each of them. Idealized computer images were used for these color samples:
|Green and yellowish green – extremely rare and highly valued colors for Spanish gem sphalerite. In green stones a very strong dispersion can be seen.|
|Pure light yellow is quite rare, and can be found mostly in small stones up to 10 ct, but very difficult in larger sphalerites. Also amazing dispersion in such stones.|
|Orange-yellow, quite common color seen in small stones. The lighter the stone the stronger the fire it displays.|
|Dark orange, the most common color. Intense and dark body color masks the dispersion, so the "fire" is not so strong, but the brilliance can be spectacular in high clarity stones.
|Pure intense orange is difficult to find, stones with medium tone and high saturation that produce an intense bright orange color are highly valued.
|Orange-red and red – rare and very highly valued colors. Like for orange stones, medium tones are the most valued, darker red stones are easier to find.|
A very particular characteristic of the sphalerite is the complex color zones, which can appear inside a single crystal, giving way to fascinating color effects. In a crystal with different color, slim red or brown layers or irregular stains can appear. These tonalities often have different directions matching up with crystalline facets and can form phantoms.
Sphalerite rough sample (5 cm width), showing color zones and irregular color distribution.
Emerald cut sphalerite with spectacular color zoning, 21.70 ct