Fluid Inclusions: Geologic Thermometers (GC-05)
Small cavities in the crystal structure of some minerals contain fluids,
typically brines, and gases. By heating a thin polished section of a
mineral specimen containing fluids under a special microscope, a
mineralogist can see the gas bubble dissolving in the brine. The
temperature at which the bubble disappears is a good indication of the
temperature at which the mineral formed. By cooling the sample and
determining the temperature at which the fluid freezes, a mineralogist can
determine the concentration of the brine.
Data from fluid-inclusion
studies show that ore minerals in mining districts and similar minerals in
Indiana were formed under similar conditions. These studies also help
explain the presence of certain minerals in Indiana coals.
Photomicrograph of fluid inclusion
Our Hoosier State Beneath Us: