Black tourmaline, scientifically known as Schorl, is a common silicate mineral recognizable by its deep, opaque black color and prismatic crystal habit. It is frequently sought after for use in jewelry, metaphysical practices, and geological collections. The mineral possesses several unusual physical characteristics, leading many to question if black tourmaline is truly magnetic in the conventional sense. Understanding the mineral’s composition and structure provides a definitive, scientific explanation for its relationship with magnetic fields.
Magnetic Classification of Black Tourmaline
Black tourmaline is not considered magnetic in the conventional sense, as a typical magnet will not attract or stick to it. Scientifically, however, black tourmaline is classified as paramagnetic, meaning it is weakly attracted to a strong magnetic field. This slight attraction is only evident when the mineral is placed near a powerful magnet, such as a rare-earth neodymium magnet. Black tourmaline exhibits the highest magnetic susceptibility among all the tourmaline varieties. While a strong magnet can cause a piece of black tourmaline to move slightly, it will never be able to hold the mineral against the force of gravity.
Tourmaline’s Unique Electrical Properties
The confusion surrounding tourmaline’s magnetic nature often stems from its remarkable electrical characteristics, which led to the name “Ceylonese Magnet” centuries ago. Tourmaline is a pyroelectric material, meaning it can generate an electrical charge when its temperature changes. Heating or cooling the crystal causes a temporary separation of positive and negative charges at opposite ends. This electrical polarization allows the crystal to attract small, light objects, such as dust particles or ash, which historically led to the mistaken belief that it was strongly magnetic.
Tourmaline is also a piezoelectric material, meaning the crystal generates an electrical charge when subjected to mechanical stress or compression. Both pyroelectricity and piezoelectricity are based on the creation of a static electrical charge due to the mineral’s unique asymmetrical crystal structure. This electrical charge is fundamentally different from the force of magnetic attraction. The charge generation capability is due to the lack of a center of symmetry within the crystal’s atomic arrangement.
Chemical Components Determining Magnetism
The weak paramagnetic response observed in black tourmaline is directly caused by its specific chemical composition. Black tourmaline is predominantly the species Schorl, an iron-rich member of the tourmaline group. The mineral’s complex chemical formula includes a high concentration of iron (Fe) within its silicate structure. This high iron content is responsible for the mineral’s opaque, deep black color, classifying it as an idiochromatic mineral.
The iron atoms present in the crystal lattice contain the unpaired electrons required to interact with a magnetic field. However, the exact arrangement of these iron atoms prevents the mineral from exhibiting strong, permanent magnetism, known as ferromagnetism. Other varieties of tourmaline, like the lithium-rich Elbaite, contain far less iron and consequently display a much weaker, or even diamagnetic, response. The iron content in Schorl dictates its magnetic susceptibility.