Black Tourmaline
Schorl (Sodium Iron-rich Tourmaline) · Semi-Precious Gemstone and Mineral Specimen.
Crystal System
Trigonal; typically occurs in elongated prismatic crystals with vertical striations, or massive/fibrous aggregates.
Mineral Group
Silicates (Cyclosilicates); Tourmaline Supergroup.
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Formation Process
Igneous/Hydrothermal: Forms in granite pegmatites and hydrothermal veins through late-stage magmatic crystallization at high pressure and moderate temperatures.
About This Crystal
Opaque, jet-black to brownish-black mineral with a glassy to sub-metallic luster. Features prominent vertical striations on crystal faces and a characteristic triangular cross-section.
Physical Characteristics
Color: Black; Streak: White to brownish; Fracture: Uneven to conchoidal; Specific Gravity: 3.0-3.25; Tenacity: Brittle; Strongly pyroelectric and piezoelectric.
Optical Properties
Refractive Index: 1.610-1.666; Double Refraction: Uniaxial negative; Birefringence: 0.018-0.040; Pleochroism: Strong (pale to dark brown).
Hardness & Durability
Origin Region
Brazil (Minas Gerais), Namibia, Madagascar, and the United States (California, Maine). Found primarily in granitic pegmatites.
Hardness & Durability
Mohs Hardness: 7 to 7.5; Toughness: Poor to Fair due to brittle nature; High durability for jewelry but prone to splintering if struck.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic or steam cleaners. Store separately from softer stones; avoid high heat and sudden temperature changes.
Rarity & Value
Common and abundant worldwide. Value is determined by crystal size, luster, and lack of fractures; typically priced between $5-$50 per kilogram for specimens.
Special Characteristics
Possesses pyroelectric and piezoelectric properties (can generate electric charge); often shows deep parallel striations and can occur with quartz or mica inclusions.
Lore & History
Historically used as a 'cleaning stone' to pull dust from screens due to its static charge. Metaphysically associated with the Root Chakra and used traditionally for protection and grounding.