Sphalerite. ( Zn,Fe ) S ), Zinc sulphide, with variable Iron content. Sphalerite is the main ore of zinc, and sometimes referred to by miners as zinc blende, or black jack. This specimen is an agglomerate of loosely cemented pieces of rock with nearly all of the surface, and all crevices, coated with small crystals of sphalerite . The crystals on the rear of the specimen are slightly larger than those on the front. The location is from the Second sun vein, Nentsberry Haggs mine, Cumbria.