tourmaline tongs

Tourmaline tongs are a simple device used to examine objects, particularly by jewelers. They consist of two transparent plates of tourmaline, cut and mounted to hold an object between them. This setup acts as a polariscope, a tool for distinguishing between glass and crystal. Tourmaline itself is a mineral known for its borosilicate composition and variable colors, including black, brown, pink, and green. Some varieties are used as gemstones. Tourmaline also exhibits piezoelectric properties, meaning it can generate an electric charge under mechanical stress or change shape when a voltage is applied, leading to its use in pressure-measuring devices.12

Light waves are transverse, with their electric fields vibrating perpendicular to the direction of propagation. Unpolarized light has electric vectors in random orientations, while polarized light has a specific relationship between the direction and magnitude of these vibrations. Tourmaline crystals are strongly dichroic, absorbing light differently depending on the viewing axis. When cut into plates parallel to the crystal's vertical axis, they allow only one direction of light (the extraordinary ray) to pass through. Placing two such plates in a crossed position blocks all light, demonstrating polarization.32