Black Tourmaline
Schorl · Semi-Precious Gemstone and Mineral Specimen
Crystal System
Trigonal, typically forming prismatic crystals with striated faces, often with a triangular cross-section.
Mineral Group
Silicates, specifically the Cyclosilicate subgroup.
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)4
Formation Process
Igneous and hydrothermal processes, typically crystallizing in pegmatites and high-temperature hydrothermal veins from boron-rich fluids.
About This Crystal
A tumbled, polished black stone with a roughly triangular shape, exhibiting a smooth, glossy, vitreous to sub-metallic luster. The body color is a solid, deep opaque black with no visible internal transparency.
Physical Characteristics
Color is black; streak is white; no distinct cleavage due to conchoidal to uneven fracture; specific gravity is approximately 3.0 to 3.2; tenacity is brittle; not magnetic.
Optical Properties
Uniaxial negative with double refraction; refractive index ranges from 1.620 to 1.698; birefringence is weak to moderate (around 0.018 to 0.040); strongly pleochroic in thin sections.
Hardness & Durability
Origin Region
Brazil, Madagascar, Pakistan, USA (California, Maine), and Russia. Forms in pegmatites, granites, and hydrothermal veins.
Hardness & Durability
Mohs hardness of 7 to 7.5; fair toughness due to lack of distinct cleavage making it prone to fracturing under severe impact; durable enough for general jewelry wear.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic and steam cleaners; store separately from softer materials; stable in light and ordinary temperatures.
Rarity & Value
Common and widely available; value depends on size, polish, and crystal form, though tumbled stones are very affordable and typically inexpensive.
Special Characteristics
Displays strong pyroelectric and piezoelectric properties, meaning it can generate an electrical charge when heated or subjected to mechanical pressure.
Lore & History
Historically used as an amulet for protection against negative energies and psychic attack. In modern crystal healing, it is associated with the root chakra and is traditionally believed to ground energy and provide a sense of security and protection.