Black tourmaline

Black tourmaline, also known as schorl, is a complex mineral belonging to the cyclosilicate group. It appears in elongated, longitudinally striated crystals, with an intense black color and vitreous luster. Its chemical composition varies but mainly includes sodium, iron, magnesium, and aluminum. It is primarily found in Brazil, Sri Lanka, and Madagascar, where it is extracted from pegmatitic rocks. Historically, it has been used as a protective stone by African tribes and medieval alchemists, who associated it with the ability to shield against negative energies. Today, it is valued for its piezoelectric and pyroelectric properties, making it useful in technological applications as well.