Large black tourmaline with hyalite

Locale: Erongo Mountain, Namibia

Approx dimensions: 3.25 x 2.5 x 2.25"

Approx weight: 645g

This large glossy black tourmaline, known as schorl, has the Mercedes termination characteristic of the Erongo region with intricate growth patterns across the faces of the tip. The sides are beautifully striated, with fine vertical lines and a chunkier accordion zig-zag to the sides of the crystal. Erongo schorl typically has very high luster as seen in this specimen.

One side of the schorl is less well-formed, with a coating of hyalite over it . There are two neat inverted hexagonal shapes in one section, remnants of quartz that once grew with the piece. Instead they are now filled with hyalite.

Hyalite is a form of opal, which in turn is part of the broader quartz family. Hyalite displays botryoidal growth (bunches of “grape-like” round crystals) with a glossy high luster like a layer of bubbles. The hyalite on this specimen has relatively small spheres, and appears off-white in contrast to the black tourmaline.

UV reactivity The small amount of hyalite will react a strong yellow-green color under 395nm UV or 365nm UV light. 395 can sometimes give hyalite an icy blue overtone, but I did not detect that with this specimen. No phosphorescence detected.