Black Tourmaline
Schorl (Tourmaline Supergroup) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal symmetry; typically appears in elongated prismatic crystals with vertical striations, but here presented in a polished spherical habit.
Mineral Group
Silicates; Cyclosilicate subgroup
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Formation Process
Igneous/Hydrothermal; forms in late-stage magmatic crystallization within pegmatites and in hydrothermal veins associated with granitic intrusions.
About This Crystal
An opaque, jet-black specimen with a high vitreous to sub-metallic luster. When polished into a sphere as shown, it displays a smooth, reflective surface without visible color zoning or inclusions to the naked eye.
Physical Characteristics
Color: Pitch black; Streak: White to grayish; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.0-3.3; Tenacity: Brittle; Fluorescence: None; Notable for being strongly pyroelectric and piezoelectric.
Optical Properties
Refractive Index: 1.610-1.666; Birefringence: 0.018-0.040; Optical Character: Uniaxial negative; Pleochroism: Strong (though difficult to see in opaque schorl); Dispersion: 0.017.
Hardness & Durability
Origin Region
Brazil, Madagascar, Namibia, and the United States (California/Maine). Primarily found in granitic pegmatites.
Hardness & Durability
Mohs Hardness: 7 to 7.5; Toughness: Fair to good; Stability: Stable to light and most chemicals, but sensitive to thermal shock.
Care & Maintenance
Wash with warm soapy water and a soft brush; avoid ultrasonic cleaners and steam cleaners due to potential internal fractures. Store away from harder gems like Topaz or Sapphire.
Rarity & Value
Common; relatively inexpensive compared to colored tourmaline. Value is based on polish quality, size, and lack of surface pits or cracks. Rarely treated.
Special Characteristics
Distinctive for its pyroelectric properties (develops an electrical charge when heated) and its ability to attract dust particles. It is the most common member of the tourmaline group.
Lore & History
Historically used as a 'mourning stone' in Victorian jewelry. In metaphysical traditions, it is considered a premier stone of protection and grounding, believed to repel negative energies and EMF radiation. Associated with the Root Chakra.