Tourmaline (likely Schorl)

Hardness: 6-7 (Mohs scale), Color: Variable, often black, dark green, brown, or sometimes blue or pink. Can be translucent to opaque. Luster: Vitreous to resinous. Crystal Structure: Hexagonal system, often forming prismatic crystals with striations parallel to the C-axis. No distinct cleavage, but can have a conchoidal or uneven fracture. Specific Gravity: 3.0-3.2.

Tourmaline forms in igneous and metamorphic rocks. It is commonly found in pegmatites (coarse-grained igneous rocks formed from late-stage magma crystallization), granites, and hydrothermal veins. It also occurs in metamorphic rocks like schists and gneisses, as well as in detrital sedimentary rocks due to its hardness and resistance to weathering. The geological age varies depending on the specific deposit, but it is found in rocks ranging from Precambrian to Cenozoic.

Gem-quality tourmaline varieties are highly valued in jewelry. Black tourmaline (Schorl) is often used for its aesthetic appeal in carvings and as a protective stone in spiritual practices. Industrial uses are limited due to its complex composition, but its piezoelectric properties have been explored in some pressure gauges and other electronic devices.

Tourmaline is known for its wide range of colors and its pyroelectric and piezoelectric properties. It can generate an electric charge when heated or pressure is applied. Different varieties of tourmaline are given specific names like Rubellite (red/pink), Indicolite (blue), Verdelite (green), Schorl (black), and Watermelon Tourmaline (pink center with green outer layer). The most common variety is Schorl (black tourmaline). It is a complex borosilicate mineral.

To identify tourmaline in the field, look for its characteristic prismatic crystals with vertical striations on the prism faces. It often has a triangular cross-section. Its hardness (harder than glass) can be tested by scratching. The color range is very broad, so other characteristics are more diagnostic. It is commonly found in pegmatite provinces around the world, including Brazil, Afghanistan, Pakistan, the United States (Maine, California), Africa (Niger, Nigeria, Mozambique), and Sri Lanka. For collectors, well-formed crystals and unusual color combinations are highly sought after.