Black Tourmaline
Schorl · Semi-Precious Gemstone and Mineral Specimen
Crystal System
Trigonal, typically forming prismatic crystals with striated vertical faces, but shown here as a tumbled and polished stone.
Mineral Group
Silicates, specifically the cyclosilicate subgroup.
Chemical Formula
NaFe2+3Al6(Si6O18)(BO33)(OH4)
Formation Process
Forms primarily through pegmatitic and hydrothermal processes, crystallizing from cooling magma rich in water and boron at high temperatures and pressures.
About This Crystal
The specimen is a tumbled, polished, opaque black stone with a smooth, glossy surface and a distinctly triangular or rounded triangular cross-section typical of tourmaline tumbled forms. It displays a vitreous to sub-metallic luster on its polished surfaces with minor surface scratches.
Physical Characteristics
Color is jet black with a colorless to white streak. It has indistinct cleavage, conchoidal to uneven fracture, a specific gravity of approximately 3.0 to 3.2, and is brittle with no significant fluorescence under UV light.
Optical Properties
Uniaxial negative with a refractive index ranging between 1.620 and 1.698. It exhibits strong birefringence and strong pleochroism in thicker, transparent crystal forms, though this tumbled piece is completely opaque.
Hardness & Durability
Origin Region
Found globally with notable deposits in Brazil, Madagascar, Pakistan, Afghanistan, and the United States (California and Maine). It forms in pegmatites and hydrothermal veins.
Hardness & Durability
Mohs hardness of 7 to 7.5. It has fair to good durability for jewelry use, though lack of cleavage makes it relatively tough, but it can be sensitive to thermal shock.
Care & Maintenance
Can be safely cleaned with warm soapy water and a soft cloth. Avoid harsh chemical cleaners, ultrasonic cleaners, and sudden extreme temperature changes.
Rarity & Value
Common. Schorl is one of the most abundant tourmaline species worldwide. Value is very low for tumbled stones and common specimens, ranging from a few dollars to tens of dollars depending on size.
Special Characteristics
Exhibits pyroelectricity and piezoelectricity, generating an electrical charge when heated or subjected to mechanical pressure.
Lore & History
Historically used as a protective amulet against negative energies and psychic attack. In modern crystal healing, it is heavily associated with the root chakra for grounding and energetic protection, though these are traditional and spiritual beliefs without scientific validation.