Schorl (Black Tourmaline)
Tourmaline var. Schorl · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal; typically prismatic with vertical striations and a triangular cross-section
Mineral Group
Silicates (Cyclosilicates)
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Formation Process
Igneous; primarily forms in granitic pegmatites and hydrothermal veins during late-stage magmatic crystallization.
About This Crystal
Opaque black mineral with a vitreous to sub-metallic luster. It often displays deep vertical striations on elongated prismatic crystals and can appear as massive or columnar aggregates within a lighter host matrix.
Physical Characteristics
Color: Deep black; Streak: White to grayish; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.0-3.2; Tenacity: Brittle; Fluorescence: None.
Optical Properties
Opaque; Refractive Index: 1.635-1.675; Birefringence: 0.018-0.040; Strongly pleochroic (usually seen in thinner sections or varieties other than Schorl).
Hardness & Durability
Origin Region
Notable sources include Brazil, Namibia, Madagascar, Afghanistan, and Pakistan. Often found in granite pegmatites.
Hardness & Durability
Mohs Hardness: 7.0-7.5; Toughness: Fair to good; highly durable for most uses but susceptible to thermal shock.
Care & Maintenance
Clean with warm soapy water; avoid ultrasonic or steam cleaners as they may cause fractures. Protect from high heat and sudden temperature changes.
Rarity & Value
Common; widely available. Value is determined by crystal size, termination quality, and presence of interesting matrix (like white quartz or lepidolite). Treatable by irradiation (though rare for black varieties).
Special Characteristics
Features vertical striations and is both pyroelectric (develops electric charge when heated) and piezoelectric (develops charge under pressure).
Lore & History
Known since ancient times, the name 'Schorl' was used before 1400. In metaphysical traditions, it is used as a stone of protection and grounding, believed to repel negative energy and clear the root chakra.