Sphalerites from the quarries of west central Illinois are predominantly intergrown, poorly formed tetrahedral crystals. Dallas City, which is along the Mississippi, normally follows the same general pattern, with tristetrahedral habits. This specimen, however, breaks the mold and is exceptional. It is a single, 2.3 cm elongated, prismatic Sphalerite on a limestone and Calcite matrix. The adamantine luster is good, and the color is a silver-black. With backlighting, you can see the dark amber color coming through the translucent crystal. I've not seen its like, for either habit, size, or quality. A very good thumbnail for the locality no question; but more importantly a superb sphalerite on a worldwide basis, as well.