MINERAL PROPERTIES: TRIBOLUMINESCENCE & THERMOLUMINESCENCE
Luminescence describes any circumstance that causes a mineral to give off light. Fluorescence is one
form of luminescence, in which fluorescent minerals glow in ultraviolet light. Triboluminescence
and thermoluminescence are two additional forms of luminescence. Triboluminescent
minerals gives off yellow or orange flashes when struck, and thermoluminescent minerals
gives off a glowing light when heated. Only few minerals are triboluminescent or
thermoluminescent, so this property is not very useful for identification. It is also
impractical to heat or strike minerals to see if they exhibit any of these properties.
However, simple testing for thermoluminescence can be done by putting a specimen in the
flame of a lighter for a short time in a dark area. If it glows for a few seconds after
the flame is removed, it is thermoluminescent. This test should only be conducted on
extra, unwanted specimens, for heating a specimen in such a way may permanently blacken
it.
To test for triboluminescence, strike the specimen with a
steel file or other tough substance in a dark area and see if sparks fly out. This test
should also only be conducted on extra specimens, since the steel file will scratch most
minerals.