Almost any type of
rock can behave as a rheid under appropriate conditions of
temperature and
pressure. For example, the
Earth's
mantle undergoes
convection over long time-scales. As the mantle supports the propagation of
shear waves, it may be deduced that it is a solid and, therefore, behaving as a rheid when it undergoes said convection.
Granite has a measured viscosity at
standard temperature and pressure of about 4.5×1019 Pa·s so it should be considered a rheid. Similarly
halite, the mineral form of
table salt, is a geological material that behaves as a rheid over relatively short time-periods. As salt is buried by other types of
sediments, it will often flow laterally towards regions of lower confining
stress. Through this mechanism,
salt domes and other structures may form. In some areas, such as the
Gulf of Mexico, these structures often serve as
traps for
petroleum and
natural gas. ==References==