Waco Gem and Mineral Club, Waco, Tx

17.2 Triboluminescence


17.2: Triboluminescence

Triboluminescence is quite a word! Kids (and adults!) may need help pronouncing it: tri΄-bō-lu-mə-nə΄-səns. The tribo part comes from the Greek word meaning "to rub." Luminescence is derived from the Latin word for "light" and is defined as low-temperature emission of light. Thus, triboluminescence is low-temperature light produced between two materials rubbed together.

In a darkened room, triboluminescence can take the form of tiny spark-like flashes observed in some minerals, like sphalerite or corundum, when a hard point is dragged across the surface. It can also occur when a mineral (or other material, like hard sugar or Wint-o-Green Life Savers) is crushed, ripped, scratched, or rubbed. Scientists still haven‘t fully explained this optical phenomenon, but they believe it to be caused by separation and reunification of electrical charges at a molecular level when bonds are broken by the rubbing or scratching. (Note that this is different from the high-temperature sparks generated when rocks and minerals like flint or pyrite are struck.)

Triboluminescence has been observed by diamond cutters, who sometimes see a diamond begin to glow while a facet is being ground. Since diamonds can be a little hard to come by, you may want to demonstrate the effect by rubbing together two large quartz crystals in a darkened room. This works best with pretty big, palm-sized specimens. You can simply rub two faces together or, to produce more light, rub the prism edge of one crystal back and forth along the prism face of the other crystal. (A prism face is one of the flat sides of the quartz crystal; the prism edge is where two flat sides come together.)

Interestingly, flashes of light have sometimes been observed during earthquakes. Some believe these 'earthquake lights' may be related to triboluminescence when rocks high in quartz content get rubbed and rendered apart during the quake.