Black Tourmaline (Schorl)

Hardness: 7-7.5 on Mohs scale. Color: Opaque black. Luster: Vitreous to resinous. Crystal structure: Trigonal; typically forms elongated prismatic crystals with vertical striations, often with a rounded triangular cross-section. Cleavage: Indistinct. Specific gravity: 3.0-3.2.

Black tourmaline forms in igneous and metamorphic rocks. It is commonly found in granites, pegmatites, and high-temperature hydrothermal veins, as well as in certain metamorphic settings like schists and gneisses. Its formation usually involves the presence of boron-rich fluids. Geological age varies widely depending on the specific deposit, ranging from hundreds of millions to billions of years old.

Black tourmaline is often used as a gemstone, though its opaque nature means it's typically cut into cabochons or beads. It's popular for metaphysical purposes, believed to offer protection and grounding. Industrially, tourmaline can be used in pressure gauges due to its piezoelectric properties, though synthetic materials are now more common for this application. It's also a significant mineral for collectors.

Black tourmaline, or Schorl, is the most common variety of tourmaline, accounting for about 95% of all natural tourmaline. The name 'tourmaline' comes from the Sinhalese word 'turamali,' meaning 'stone with mixed colors,' though Schorl specifically refers to the black variety. Ancient Egyptians believed that tourmaline traveled from the Earth's center to the sun and collected all colors of the rainbow along the way.

To identify black tourmaline in the field, look for its distinctive opaque black color, vitreous luster, and characteristically long, striated prismatic crystals, often with a triangular cross-section. It is quite hard, so it will scratch glass. It's commonly found in granite-rich areas, pegmatite dikes, and metamorphic terrains worldwide, including Brazil, Africa, Pakistan, and the USA (Maine, California). Collectors often seek well-formed, terminated crystals. The specimen in the image appears to be a tumbled or water-worn piece of black tourmaline, characterized by its dark, polished appearance.