Black Tourmaline

Hardness: 7-7.5 on Mohs scale. Color: Opaque black. Luster: Vitreous to resinous. Crystal structure: Trigonal (often as prismatic crystals with vertical striations). Cleavage: None, exhibits conchoidal or uneven fracture. Specific Gravity: 3.06-3.26.

Black tourmaline, or Schorl, typically forms in igneous and metamorphic rocks. It crystallizes from hydrothermal fluids during the late stages of magmatic differentiation in pegmatites and granites, or through regional metamorphism in schists and gneisses. Its formation age varies widely depending on the geological event.

Black tourmaline is widely used as a gemstone, particularly for beads, cabochons, and carvings. Due to its pyroelectric and piezoelectric properties, it has industrial uses in certain pressure gauges and electronic devices, though less commonly than quartz. It's also popular for its perceived metaphysical properties.

Tourmaline is a complex borosilicate mineral group. Schorl is the most common variety, accounting for about 95% of all natural tourmaline. The name 'tourmaline' comes from the Sinhalese word 'turamali,' meaning 'stone with mixed colors,' though Schorl is exclusively black. It can generate an electrical charge when heated or subjected to pressure.

In the field, black tourmaline is identified by its intense black color, vitreous luster, often columnar or acicular crystal habit with characteristic vertical striations, and its hardness (it can scratch glass). It's commonly found in granite pegmatites, metamorphic rocks, and sometimes in placer deposits. Major localities include Brazil, Africa (e.g., Namibia, Tanzania), the United States (e.g., Maine, California), and Pakistan. For collectors, look for well-formed crystals and pieces suitable for lapidary work.