Black Tourmaline (Schorl)
Schorl (Sodium iron aluminum borosilicate) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal symmetry; habit is typically prismatic with vertical striations, often occurring in massive or columnar aggregates.
Mineral Group
Silicates (Cyclosilicates); Tourmaline Supergroup.
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Formation Process
Primarily Igneous; forms via magmatic crystallization in pegmatites through hydrothermal activity and boron-rich fluid cooling in cavities.
About This Crystal
An opaque black specimen with a vitreous to sub-metallic luster. The surface shows characteristic longitudinal striations and uneven, brittle fracture surfaces with occasional golden-metallic flashing due to inclusions or surface light interference.
Physical Characteristics
Color: Jet black; Streak: White to grayish; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.06–3.20; Fluorescence: None; Notable for vertical parallel grooves on prism faces.
Optical Properties
Opaque; Refractive Index: 1.614–1.666; Birefringence: 0.018–0.040; Characterized by strong pleochroism in thinner sections (though generally appears solid black). Uniaxial negative.
Hardness & Durability
Origin Region
Notable sources include Brazil (Minas Gerais), Namibia, Madagascar, Afghanistan, and the United States (California, Maine). Found in granitic pegmatites and metamorphic rocks.
Hardness & Durability
Mohs hardness: 7.0–7.5. Good toughness for a mineral, though brittle. High durability for jewelry and display specimens.
Care & Maintenance
Safe to clean with warm soapy water and soft brushes. Generally stable, but can be damaged by extreme heat or ultrasonic cleaners if it contains significant inclusions/fractures.
Rarity & Value
Common and abundant. Value is determined by crystal termination quality, size, and presence of interesting inclusions. Generally affordable unless in large, museum-grade terminated crystals.
Special Characteristics
Strongly Pyroelectric (develops electric charge when heated) and Piezoelectric (develops charge under pressure). Displays deep vertical striations on crystal faces.
Lore & History
Historically used as a 'mourning stone' in Victorian jewelry. In lore, it is regarded as a premier stone of protection and grounding, associated with the Root Chakra and believed to repel negative energies.