radiation, the samples give only one natural thermoluminescence peak at ap- 

 proximately 310C. After irradiation, both calcite and dolomite gave three well- 

 defined peaks at 120C, 240C, and 310C. In calcite, the peak at 120C is much 

 larger than it is in dolomite. The ratio of the peaks can be used to determine the 

 percentage of calcite and dolomite in the rocks. MgC0 3 by itself has very little 

 thermoluminescence. 



30 r 



I 2 3 



THERMOLUMINESCENCE PEAK 1/ PEAK 2 



Figure 10-9. Relation of thermoluminescence to magnesium content of limestone. 



OTHER MINERALS Calcium fluoride in the form of fluorite min- 



erals exhibits bright thermoluminescence after 

 exposure to gamma rays or X-rays. Many fluorites have uranium as an impurity, 

 or they have been exposed to gamma rays from adjacent radioactive minerals 

 for geological ages so that they exhibit bright natural thermoluminescence and 



193 



