Black Tourmaline
Schorl (Sodium Iron Aluminum Borosilicate Hydroxide) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal; commonly occurs as elongated prismatic crystals, often with heavy vertical striations and a triangular cross-section.
Mineral Group
Silicates; Cyclosilicate (Tourmaline Group)
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3OH
Formation Process
Primarily Igneous-Pegmatitic, formed from boron-rich fluids during the final stages of magma crystallization. It also forms in Metamorphic environments via hydrothermal replacement.
About This Crystal
An opaque, jet-black mineral with a vitreous to sub-metallic luster. The specimen appears as a rough, fractured mass showing characteristic parallel striations along the crystal faces and a dense, light-absorbing surface.
Physical Characteristics
Color: Black; Streak: White to brownish-black; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.0-3.25; Tenacity: Brittle; Fluorescence: None; Notable for strong piezoelectricity and pyroelectricity.
Optical Properties
Refractive Index: 1.610-1.666; Birefringence: 0.018-0.040; Pleochroism: Strong (shades of dark brown/black); Uniaxial negative optics; Opaque in thick sections.
Hardness & Durability
Origin Region
Mainly found in Brazil, Namibia, Madagascar, Afghanistan, and the USA (California and Maine); typically found in granite pegmatites and metamorphic rocks like schists.
Hardness & Durability
Mohs Hardness: 7 to 7.5; Toughness: Fair to Good; High durability and chemical stability; excellent for all types of jewelry.
Care & Maintenance
Safe to clean with warm soapy water or ultrasonic cleaners. Avoid sudden temperature changes. Highly stable under sunlight and most household chemicals.
Rarity & Value
Common and abundant worldwide. Value is generally low for rough specimens but increases for high-luster terminated crystals. Treatments are rare for Schorl as its color is naturally deep black.
Special Characteristics
Demonstrates pyroelectricity (develops electrical charge when heated) and piezoelectricity (develops charge under pressure). Vertical striations are a primary diagnostic feature.
Lore & History
Historically used as a 'mourning stone' in Victorian jewelry. In metaphysical lore, it is considered the premier stone of protection against negative energy and is associated with the Root Chakra. Known in pre-modern times as 'Aschentrekker' (ash puller) in Dutch for its ability to attract ash via static electricity.