Black Tourmaline (Schorl)
Schorl (Sodium Iron Aluminum Borosilicate Hydroxide) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal. Habit is typically prismatic with vertical striations; may also be massive or acicular.
Mineral Group
Silicates (Cyclosilicates); Tourmaline Group
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Formation Process
Primarily Igneous (pegmatitic) or Metamorphic. Forms through crystallization of molten rock or hydrothermal activity at high pressures.
About This Crystal
Opaque black specimen with a vitreous to sub-metallic luster. Features characteristic heavy vertical striations and deep coal-black coloration. Often found in rough, columnar, or fractured aggregate forms.
Physical Characteristics
Color: Black; Streak: White to brownish; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.0-3.25; Fluorescence: Usually none; Tenacity: Brittle.
Optical Properties
Opaque (no light transmission in large specimens); Refractive Index: 1.614-1.666; Birefringence: 0.018-0.040; Uniaxial negative.
Hardness & Durability
Origin Region
Brazil, Madagascar, Namibia, Afghanistan, and the United States (Maine/California). Found in granitic pegmatites and metamorphic rocks.
Hardness & Durability
Mohs hardness: 7.0–7.5. Good durability for jewelry, though brittle nature makes it prone to chipping if struck.
Care & Maintenance
Clean with warm soapy water. Generally safe in ultrasonic cleaners but avoid steam cleaning due to liquid inclusions. Store away from heat and strong acids.
Rarity & Value
Common and abundant. Value is determined by crystal size, termination quality, and luster. Rough specimens are very affordable.
Special Characteristics
Strongly Pyroelectric (develops electric charge when heated) and Piezoelectric (develops charge under mechanical stress). Extremely high iron content provides the black color.
Lore & History
Historically known in Europe since the 1400s; used as 'Ashentrekker' by the Dutch to pull ash from pipes. Traditionally associated with grounding, protection from negative energy, and the Root Chakra.