Black Tourmaline
Sodium iron aluminum borosilicate (schorl)
The opaque black iron-rich variety of tourmaline (schorl), forming striated prismatic crystals popular as a protective grounding stone.
- Mohs hardness
- 7-7.5
- Color
- Opaque black
- Type
- mineral
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Overview
Black tourmaline, known mineralogically as schorl, is the iron-rich, opaque black member of the large tourmaline group of borosilicate minerals. It is by far the most common tourmaline and the source of most black crystals sold as 'tourmaline.'
It forms hard, lustrous prismatic crystals with characteristic lengthwise striations and a rounded-triangular cross-section. Tourmaline is also notable for being pyroelectric and piezoelectric—it develops an electric charge when heated or stressed, which can attract dust and ash.
While the colorful tourmalines (pink, green, watermelon) are gem-quality, schorl is mainly a collector and metaphysical stone.
Formation & geology
Black tourmaline (schorl) crystallizes mainly in granitic pegmatites and granites, where boron-rich residual melts and fluids allow tourmaline to grow. It also occurs in metamorphic rocks such as schists and gneisses, and in hydrothermal veins.
Its iron content makes it black, in contrast to the lithium- and manganese-bearing tourmalines that produce gem colors. Schorl is durable and resists weathering, so it often survives as crystals in sands and placer deposits.
Notable sources include Brazil, Africa (Namibia, Madagascar), Pakistan, and the USA (Maine, California).
How to identify it
- Color: Opaque, deep black with a vitreous to slightly resinous luster.
- Crystal form: Elongated prisms with strong vertical striations and a rounded triangular cross-section—very diagnostic.
- Hardness: 7-7.5; scratches glass and resists a steel knife.
- Fracture: Uneven; no good cleavage.
Look-alikes: Black obsidian is glassy and conchoidal, not striated prisms. Hornblende and augite are softer and have cleavage. Onyx is banded chalcedony. The striated prismatic habit and high hardness distinguish schorl.
Uses & significance
Most black tourmaline is sold as specimens, tumbled stones, and beads rather than fine jewelry, though striated crystals are popular with collectors and sometimes set in rustic designs.
Industrially, tourmaline's piezoelectric and pyroelectric properties have been used in pressure gauges and some niche electronic applications.
In metaphysical traditions black tourmaline is one of the most popular 'protection' and 'grounding' stones, believed to shield against negativity and electromagnetic energy—these are cultural beliefs, not scientifically demonstrated effects.
Frequently asked questions
What is the difference between black tourmaline and schorl?
They are the same thing—schorl is the mineralogical name for the common iron-rich black variety of tourmaline.
How do you tell black tourmaline from obsidian?
Black tourmaline forms striated prismatic crystals and is harder (7-7.5), while obsidian is glassy with smooth conchoidal fracture and no crystal faces.
Is black tourmaline valuable?
Schorl is common and inexpensive, unlike the rare gem tourmalines. Value comes mainly from well-formed crystals and attractive matrix specimens.
Does black tourmaline really block EMF?
There is no scientific evidence that it blocks electromagnetic fields. EMF protection is a metaphysical belief, not a measurable physical property.
Black Tourmaline guides
In-depth guides for identifying, valuing, and understanding Black Tourmaline.
