Black Tourmaline
Schorl (Sodium Iron Aluminum Borosilicate) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal; typically occurs as elongated prismatic crystals with vertical striations, often triangular in cross-section.
Mineral Group
Silicate; Cyclosilicate (Tourmaline group)
Chemical Formula
NaFe3Al6(BO3)3Si6O18(OH)4
Formation Process
Igneous and Metamorphic; typically formed in pegmatites and granites by the crystallization of magma or through hydrothermal activity in late-stage magmatic fluids.
About This Crystal
Black, opaque specimen with a high vitreous (glassy) to sub-metallic luster. The surface shows characteristic vertical striations and uneven, conchoidal fractures. It appears dense and solid with no transparency.
Physical Characteristics
Color: Jet black; Streak: White to grayish; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.0–3.25; Tenacity: Brittle; Fluorescence: Generally none.
Optical Properties
Refractive Index: 1.614–1.666; Birefringence: 0.018–0.040; Pleochroism: Strong (though difficult to see in opaque specimens); Optically Uniaxial (-).
Hardness & Durability
Origin Region
Brazil, Namibia, Pakistan, Madagascar, and various regions of the United States. Found commonly in granitic pegmatites.
Hardness & Durability
Mohs Hardness: 7 to 7.5; Toughness: Fair to good; Stability: Stable to light and chemicals, but can be sensitive to thermal shock (rapid temperature changes).
Care & Maintenance
Wash with warm soapy water and a soft brush. Safe for ultrasonic cleaning if no fractures are visible. Avoid steam cleaning and extreme heat. Store away from softer stones to prevent scratching them.
Rarity & Value
Common; Schorl is the most abundant member of the tourmaline group. It is inexpensive compared to colorful varieties, though high-quality aesthetic luster increases collector value.
Special Characteristics
Strongly Pyroelectric (develops electric charge when heated) and Piezoelectric (develops charge under mechanical stress). Features vertical striations along the crystal length.
Lore & History
Historically used as a 'mourning stone' in jewelry. In metaphysical lore, it is regarded as a premier stone for 'grounding' and 'protection' from negative energy and EMF radiation.