Tourmaline from Nigeria has been known in the gem trade since at least the middle 1980s (see, e.g., Gem News: Spring 1988, p. 59; Spring 1989, p. 47; Spring 1992, p. 62). These stones originated from tin-bearing pegmatites in Kaduna State, as well as from a pegmatite belt southeast of Kaffi in central Nigeria (J. Kanis and R. R. Harding, 'Gemstone prospects in central Nigeria,' Journal of Gemmology, Vol. 22, No. 4, 1990, pp. 195-202). Gem-quality green, red, pink, and bicolored tourmalines have been recovered. Recently, contributing editor Karl Schmetzer provided information on a recent tourmaline find in Nigeria.

In summer 1998, Nigerian traders at Idar-Oberstein offered large parcels of gem tourmaline from a locality west of the town of Ogbomosho, near the border with the country of Benin. More than 100 rough crystals and 10 faceted stones were loaned to Dr. Schmetzer by Karl Egon Wild Co. (Kirschweiler) and Julius Petsch Jr. Co.(Idar-Oberstein). Dr. Schmetzer described the crystals as prismatic in habit (figure 15), with trigonal prism faces m {0110} and hexagonal prism faces a {1120}; the dominant trigonal pyramid faces were o {0221}, sometimes in combination with ditrigonal pyramid x {1232} faces. The relative size of the terminal facet, or pedion, c (0001) varied from small to large (figure 16).

Most of the crystals were color zoned purplish red to pink to nearly colorless. In some samples, the growth zones adjacent to the pedion (parallel to the pyramid faces) were medium to intense yellowish green or green; rarely, this end of a crystal was bluish gray in color (again, see figure 15). The pleochroism for the red and pink zones was colorless to medium pink parallel to the c-axis, and intense pink to red perpendicular to the c-axis. For green zones, it was light yellowish green parallel to the c-axis, and intense yellowish green or green perpendicular to this axis. For the bluish gray zones, pleochroism was light grayish blue parallel to the c-axis, and intense grayish blue perpendicular to this axis.

The faceted stones were evenly colored red or pink (figure 17), bicolored green and pink (and, rarely, blue and pink), or color zoned. The refractive indices and specific gravities varied within small ranges: n_w = 1.640 and n_E = 1.620 (both ± 0.002); specific gravity = 3.05 ± 0.02. On the basis of visible absorption spectroscopy, Dr. Schmetzer determined that Mn³⁺ was the dominant chromophore in the red and pink samples.