The spring thus formed keeps the tourmaline disks together and, tightly held between them, the slice of the sample to be analysed, which is usually held in a cork frame.
The name of the instrument derives from its shape, which is that of tongs.
Tourmaline tongs are the simplest kind of polariscope for observing chromatic polarization phenomena in crystalline plates both in parallel and convergent light.
For observation in parallel light, the observer's eye must see the sample between the tourmaline disks at the distance of distinct vision (about 20 cm) in front of a well-lit background, such as a white wall in full sunlight.
For observation in convergent light, the observer must see the background through the tongs held to the eye.
Tourmaline tongs present a coloured field which causes some difficulty in observation and for this reason they were completely replaced, even in the field of mineralogy, by the Nicol prism analyser.