Black opaque ilmenite with clear quartz, greenish chlorite and high-relief apatite. In rock thin section, viewed in plane-polarized light. Ilmenite grains are about 2 mm in longest dimension. Opelt Quarry, Clark County, Wisconsin. (Photo by W. Cordua.) Ilmenite is a black metallic mineral occurring in tabular crystals or platy masses. It is found as an …