Schorl (Black Tourmaline)
Schorl (IMA: Schorl) belonging to the Tourmaline Supergroup · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal; typically prismatic with vertical striations, often appearing massive or columnar.
Mineral Group
Silicates; specifically Cyclosilicates containing boron.
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Formation Process
Igneous; forms during the late-stage crystallization of granitic pegmatites or via hydrothermal and metamorphic processes involving boron-rich fluids.
About This Crystal
Opaque, jet-black to brownish-black mineral with a vitreous to sub-metallic luster. It often displays deep vertical striations on elongated prismatic faces and may show uneven to conchoidal fractures.
Physical Characteristics
Color: Black; Streak: White to grayish; Cleavage: Poor/Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.0-3.25; Tenacity: Brittle; Notable piezoelectricity and pyroelectricity.
Optical Properties
Opaque (though thin slivers may be translucent); Refractive Index: 1.614-1.666; Birefringence: 0.018-0.040; Strongly pleochroic in thin sections.
Hardness & Durability
Origin Region
Notable sources include Brazil, Namibia, Pakistan, and the USA (California and Maine); found in granitic pegmatites and metamorphic rocks.
Hardness & Durability
Mohs Hardness: 7 to 7.5; High durability, though brittle and prone to shattering upon hard impact along fracture lines.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic or steam cleaners due to potential internal fractures; keep away from extreme heat.
Rarity & Value
Abundant and common relative to other tourmalines; value depends on crystal size and termination perfection; usually very affordable as specimens.
Special Characteristics
Exhibits strong piezoelectricity (charges under pressure) and pyroelectricity (charges when heated); vertical striations are characteristic.
Lore & History
Historically used as 'mourning jewelry' in the Victorian era; traditionally associated with grounding and protection from negative energy in modern metaphysical practices.