Thermoluminescence
Thermoluminescence is light given off by a mineral when heated, used to measure petrologic subtype and terrestrial age.
When certain minerals, especially feldspar, are exposed to radiation, electrons become trapped in defects in their crystals. Heating the crystal releases the electrons, which give off a faint glow. This is thermoluminescence, or TL.
In meteoritics TL has two main uses. First, the sensitivity of a chondrite's TL depends on how much crystalline feldspar it contains. In the most primitive type 3 chondrites, feldspar is still glass, so TL is weak; with more heating, more feldspar crystallises and TL grows stronger. This allowed researchers in 1980 to define subtypes from 3.0 to 3.9 for ordinary chondrites.
Second, natural TL builds up from cosmic rays while a meteoroid is in space and then fades slowly once it is on Earth. Measuring the remaining natural TL helps estimate how long a meteorite has been on the ground, and whether it passed close to the Sun, where heating would have emptied the traps.
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Level: Expert Advanced