Schorl is the iron-rich member of the tourmaline group and makes up the large majority of all tourmaline on Earth. It is opaque black, with a glassy luster and long, striated crystals. Jewelers have used it for mourning jewelry, beads and modern cabochons, and it played a part in the scientific discovery of electrical effects in crystals.
What schorl is
Tourmaline is a group of borosilicate minerals that share one crystal structure but differ in chemistry. The gem species elbaite contains lithium and comes in pink, green and blue. Schorl contains iron in place of lithium. That iron absorbs light so strongly that schorl looks black and opaque, except in very thin slices, where it can show a dark brown or blue.
Schorl forms a series with elbaite and with dravite, the magnesium-rich tourmaline. The table shows how the main species differ.
| Species | Defining elements | Typical colors |
|---|---|---|
| Schorl | Sodium and iron | Black |
| Elbaite | Sodium, lithium and aluminum | Pink, red, green, blue, colorless, multicolor |
| Dravite | Sodium and magnesium | Brown, yellow-brown, black |
| Liddicoatite | Calcium and lithium | Multicolor, often zoned |
| Uvite | Calcium and magnesium | Green, brown |
Crystals often grade from one species to another. Some show a black schorl base topped with colored elbaite.
The name schorl is old. It comes from a German mining term in use by the 16th century, and some sources link it to the village of Zschorlau in Saxony. It is one of the oldest mineral names still in use.
Crystals and identification
Schorl crystals are long prisms with a rounded triangular cross-section, a typical tourmaline shape. Deep grooves run along the length of each crystal. Crystals can be thumb-sized or many centimeters long. Schorl also forms radiating sprays and needles inside quartz, which produces tourmalinated quartz.
It breaks with a conchoidal to uneven fracture and has no useful cleavage. Black look-alikes include onyx, jet, obsidian, black spinel, hematite and black glass. The grooved prism shape is the easiest clue in rough material. Polished stones can be told apart by refractive index, specific gravity and hardness.
Where schorl forms
Schorl is common in granite and granite pegmatites. It also occurs in metamorphic rocks such as schists and gneisses, where boron-rich fluids react with surrounding rock. The igneous rocks and gemstones page explains how pegmatites concentrate boron, lithium and other rare elements.
Schorl is mined in Brazil, Pakistan, Namibia, Madagascar, the United States, Russia and many other countries. Fine specimen crystals come from Namibia's Erongo Mountains and from Pakistan.
Schorl in jewelry
Black tourmaline appears as cabochons, beads, rough crystal pendants and occasionally faceted stones. Faceted schorl has a bright, glassy black surface similar to black spinel. Because it is opaque, cutters favor shapes that show its luster.
Schorl has a hardness of 7 to 7.5, harder than jet or onyx, and works in most jewelry types.
Mourning jewelry
In the Victorian era, people wore black jewelry after a death in the family. Queen Victoria's long mourning for Prince Albert after 1861 made black jewelry fashionable in Britain. Whitby jet was the favorite material, but jewelers also used black glass (sold as French jet), onyx, vulcanite and black tourmaline. The Victorian jewelry page covers mourning jewelry more fully.
Schorl was a less common choice than jet, but its hardness and sheen made it useful for faceted mourning pieces.
Pyroelectricity and piezoelectricity
Tourmaline crystals develop opposite electrical charges at their two ends when heated or cooled. This is pyroelectricity. Dutch traders in the 18th century noticed that warm tourmaline attracted and then repelled ash, and it earned the Dutch name aschtrekker, or ash puller. Scientists in the 18th century, including Franz Aepinus, studied the effect in tourmaline.
In 1880 the brothers Pierre and Jacques Curie showed that squeezing certain crystals, including tourmaline and quartz, produces an electric charge. This is piezoelectricity. Tourmaline was among the crystals the Curies used in their experiments. During the 20th century, tourmaline was used in pressure gauges, including devices that measured blast pressures, because it responds to pressure from all directions. Quartz later became the standard piezoelectric crystal for oscillators and electronics.
These are physical properties of the crystal. They do not imply any effect on the wearer, and any such claims are folklore.
Durability and care
Schorl is hard and fairly tough. It has no cleavage, but crystals can break across their length. Clean it with warm soapy water. Avoid ultrasonic cleaners for rough crystal pendants or stones with fractures. Warm schorl can attract dust because of its pyroelectric property, and a damp cloth removes it. The guide to cleaning jewelry safely has general advice, and the gemstone durability page compares wearability.
Schorl is rarely treated. Some cheap black stones sold as tourmaline are dyed or are a different material, so buy from sellers who identify their stones.
Frequently asked questions
Is black tourmaline the same as schorl?
Most black tourmaline is schorl. Some black tourmaline is dravite or another species, but gem and bead material sold as black tourmaline is usually schorl.
Is schorl expensive?
Schorl is the most common tourmaline and is inexpensive. Fine, large specimen crystals are worth more to collectors than jewelry material.
Can black tourmaline be faceted?
Yes. Faceted schorl shows a bright black luster, though most of it is cut as cabochons and beads.
Why does black tourmaline attract dust?
Tourmaline is pyroelectric. Temperature changes create a small electric charge on the crystal, which can pull dust toward it.