Black Tourmaline
Schorl · Mineral Specimen and Decorative Stone
Crystal System
Trigonal system, typically forming prismatic crystals with characteristic longitudinal striations and a triangular or rounded triangular cross-section.
Mineral Group
Silicates, specifically the cyclosilicate subgroup.
Chemical Formula
NaFe2+3Al6(Si6O18)(BO3)3(OH)4
Formation Process
Primarily forms through magmatic-hydrothermal processes in granitic pegmatites and pneumatolytic stages of igneous intrusion, often at high temperatures and pressures.
About This Crystal
The specimen is an opaque, deep black elongated crystal fragment exhibiting prominent parallel vertical striations along its prism faces. It has a sub-metallic to vitreous luster and rough, broken terminations.
Physical Characteristics
Color is solid black with a white streak. It has no true cleavage, instead breaking with an uneven to conchoidal fracture. Specific gravity ranges from 3.0 to 3.2. Tenacity is brittle. It can exhibit pyroelectricity and piezoelectricity.
Optical Properties
Uniaxial negative with strong pleochroism, though opaque varieties like schorl show little visible light transmission. Refractive index ranges from approximately 1.620 to 1.698 with a birefringence around 0.018 to 0.040.
Hardness & Durability
Origin Region
Found globally with notable sources in Brazil, Pakistan, Madagascar, the United States (California and Maine), and Russia. Typically forms in granite pegmatites and hydrothermal veins.
Hardness & Durability
Mohs hardness of 7 to 7.5. It has fair toughness, but lacks cleavage planes which makes it less prone to splitting than some other stones, though it is still brittle.
Care & Maintenance
Can be cleaned safely with warm soapy water and a soft brush. Avoid ultrasonic and steam cleaners. Store separately to prevent scratching softer stones. Resistant to most chemicals and not sensitive to fading from sunlight.
Rarity & Value
Common. Widely available worldwide. Value is generally low to moderate, depending primarily on the size, perfection, and aesthetic appeal of the crystal matrix specimen.
Special Characteristics
Exhibits strong pyroelectric and piezoelectric properties, generating an electric charge when heated or compressed. Distinct longitudinal striations are a signature morphological feature.
Lore & History
Historically used as a protective talisman against negative energies and psychic attack. In modern crystal healing, it is heavily associated with the Root Chakra for grounding, protection, and clearing energetic blockages. These are traditional beliefs and not scientifically proven claims.