Schorl (Black Tourmaline)
Tourmaline var. Schorl · Mineral Specimen and Semi-Precious Gemstone
Crystal System
Trigonal; typically prismatic, elongated crystals with vertical striations, frequently occurring in massive or columnar aggregates.
Mineral Group
Silicates; Cyclosilicate subgroup
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH)
Formation Process
Igneous; primarily forms through magmatic crystallization in pegmatites and late-stage hydrothermal processes.
About This Crystal
Opaque, deep black crystals with a vitreous to sub-metallic luster. Visible in the image are fractured, irregular masses and smaller needle-like inclusions within a lighter matrix, showing characteristic striations and a vitreous sheen.
Physical Characteristics
Color: Jet black; Streak: White to brownish; Cleavage: Indistinct; Fracture: Conchoidal to uneven; Specific Gravity: 3.0-3.2; Non-fluorescent under UV light.
Optical Properties
Opaque; refractive index is approximately 1.63-1.66; displays strong dichroism when thin sections are viewed; no optical phenomena like chatoyancy visible in this massive specimen.
Hardness & Durability
Origin Region
Notable sources include Brazil, Namibia, Pakistan, and the United States (Maine, California). Typically found in granitic pegmatites.
Hardness & Durability
Mohs Hardness: 7 to 7.5; Toughness: Fair to good, though brittle; highly stable and resistant to most chemicals and fading.
Care & Maintenance
Clean with warm soapy water; ultrasonic and steam cleaners are generally safe but avoid if fractures are present; store separately to prevent scratching softer stones.
Rarity & Value
Common and abundant; value is generally low for massive specimens, increasing for well-formed terminal crystals. Untreated.
Special Characteristics
Strongly piezoelectric and pyroelectric (develops electric charge when squeezed or heated); often contains rutilated or phantom inclusions in associated quartz.
Lore & History
Historically used as a 'mourning stone' in Victorian jewelry. In lore, it is considered a premier stone for protection and grounding, associated with the Root Chakra.