Internal characteristics

Sphalerite commonly presents multiple fluid inclusions in form of veils, fingerprints or feathers. Two-phase liquid-vapor fluid inclusions with predominance of the liquid phase and small vapour bubble are the most common. Fluid inclusions often have negative crystals forms and sometimes reach large sizes.  These inclusions are easily appreciated in exfoliated crystals were cleavage planes give perfect visibility inside the stone, and also in faceted sphalerites.

Biphasic inclusions in sphalerite

Two-phasefluid inclusions with liquid phase and vapor bubbles in faceted sphalerite. Field of view 4 mm.

Interconnected fluid inclusions

Veil of interconnected fluid inclusions in faceted sphalerite. Field of view 4 mm.

Color zones in twinned sphalerite

Complex color zoning in sphalerite. Vertical lines correspond to twinning planes. Field of view 3 mm.

In some sphalerites, tiny primary fluid inclusions can be distributed uniformly inside the stone or they can in some areas in its interior. These localized inclusions can mark some stages of the growth of the crystal, and can affect its transparency, from low turbidity to a translucent material.

Sphalerites virtually inclusions free are extremely rare; normally almost all faceted stones present some veils or fissures visible to the naked eye. The quantity of inclusions is extremely important for the valuation of sphalerites. Within the same color range, the price per carat for eye-clean stones is several times higher than for those with different quantities of inclusions.

Some examples of different clarity grades of Spanish gem sphalerites:

Clarity faceted sphalerite
1. Example of eye-clean stone (diameter 12 mm). Although some inclusions can be visible on the amplified photo, the stone is totally clean to the naked eye.

Clarity faceted sphalerite
2. Some minor inclusions difficult to see to the naked eye. Such inclusions do not affect the brilliance of the stone.
Clarity faceted sphalerite
3. Some inclusions quite easily seen to the naked eye, slightly affecting the brilliance in some small areas.
Clarity faceted sphalerite
4. Inclusions easily seen to the naked eye, situated in a large portion of the volume of the stone and reducing brilliance of the stone.

Clarity faceted sphalerite
5. Small inclusions in all the volume of the stone, the transparency of the stone is strongly affected but it conserves some brilliance.

Clarity faceted sphalerite
6. Large reflective fractures and clouds of inclusions in all the volume of the stone. Very low internal brilliance, the reflection of light from the pavilion facets is only visible in some areas.