Black Tourmaline
Schorl · Semi-Precious Gemstone and Mineral Specimen
Crystal System
Trigonal. Exhibits columnar, prismatic crystals often with striated faces and a characteristic rounded triangular cross-section.
Mineral Group
Silicates, specifically the Cyclosilicate subgroup
Chemical Formula
NaFe2+3Al6(Si6O18)(BO33)(OH4)
Formation Process
Igneous and hydrothermal processes, typically crystallizing from cooling magmatic fluids rich in boron and water within pegmatites and metamorphic rocks.
About This Crystal
The specimen is a tumbled, dark black stone with a polished surface, opaque transparency, and a vitreous to sub-metallic luster. The characteristic rounded triangular shape reflects the internal trigonal symmetry and typical cross-section of tourmaline crystals.
Physical Characteristics
Color is deep black with a white streak. It has no true cleavage, exhibiting an uneven to conchoidal fracture. Specific gravity ranges from 3.0 to 3.2. Tenacity is brittle. It displays strong pyroelectricity and piezoelectricity.
Optical Properties
Refractive index ranges from 1.620 to 1.650 with negative birefringence. It is doubly refractive and typically displays strong pleochroism in raw, transparent varieties, though black tourmaline (schorl) is generally opaque.
Hardness & Durability
Origin Region
Notable sources include Brazil, Pakistan, Afghanistan, Madagascar, and the United States (Maine and California). Forms mainly in pegmatites, granites, and hydrothermal veins.
Hardness & Durability
Mohs hardness of 7 to 7.5. It has fair to good toughness and is relatively stable, making it suitable for most types of jewelry when properly set.
Care & Maintenance
Can be cleaned safely with warm soapy water and a soft brush. Avoid ultrasonic cleaners and harsh chemicals. Store separately from softer gems to prevent scratching.
Rarity & Value
Common and widely available. Value is generally low for standard polished pieces, though exceptionally well-formed crystal clusters can command higher prices among collectors. Treatments are rare and usually unnecessary.
Special Characteristics
Exhibits pyroelectric and piezoelectric properties, meaning it generates an electrical charge when heated or subjected to mechanical pressure.
Lore & History
Historically used as a protective amulet against negative energies and earth demons in ancient cultures. In modern metaphysical practices, it is associated with the Root Chakra and is widely believed to provide grounding, psychic protection, and energetic shielding.