Rough selection

Even in Áliva mine, where the best gem sphalerite in the world was found, only few stones are suitable for faceting. That’s why a careful rough selection must be carried out before cutting.

A powerful lamp is used to determine the transparent areas of the rough, which could eventually become gem quality after proper faceting. Rough surfaces usually are quite opaque in other gems, so faceters usually polish small “windows” in one or more sides of the stone to see its internal transparency, inclusions and color zoning. Excellent cleavage of sphalerite is very helpful for finding areas suitable for faceting, cleavage planes act as natural windows which allow to see the internal world of the stones.

Large pieces with opaque areas and fissures have to be sawed or broken following natural cleavage fractures, to get smaller pieces and make a final selection of material suitable for faceting. Sometimes, from huge sphalerite samples separated in little blocks, only few small stones can be faceted, if any.

Of course, larger faceted stones are more rare and valuable, but large sphalerites full of inclusions and fractures are much less attractive than small clean and sparkly sphalerites. That’s why a very careful rough selection, grading and preparation are needed before cutting.

Some selected rough sphalerite is available in this section of our website.

Selected rough sphalerite ready for faceting, pieces ranging from 1 to 3 cm.

Selected rough sphalerite for faceting, pieces ranging from 1 to 2 cm.

Studying a unique piece of sphalerite rough before cutting, 1190 carats weight!