In addition, Rb is a highly incompatible element that, during partial melting of the mantle, prefers to join the magmatic melt rather than remain in mantle minerals. The radiogenic daughter, Sr, is produced in this decay process and was produced in rounds of stellar nucleosynthesis predating the creation of the Solar System.
However, because Rb substitutes for K in minerals and these minerals have different K/Ca ratios, the minerals will have had different Rb/Sr ratios.
During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase.
Thorium is added to magnesium and magnesium alloys to improve their high-temperature strength.
It has been used in commercial photoelectric cells for measuring ultraviolet light of wavelengths ranging from 2000 to 3750 angstroms.
The metal may be extruded, rolled, forged, swaged, and spun, but drawing is difficult because of thorium’s low tensile strength.