This linked website discusses the background and flight of the instrument and also provides some interesting spectral emissivity curves for Quartz (SiO2), Feldspar* and Hornblende** and an equal mixture of the two,

The TES instrument first flew aboard the Mars Observer spacecraft that was lost. The TES instrument was rebuilt and launched along with instruments aboard the new Mars Global Surveyor spacecraft.

The purpose of the TES device is to measure the spectral distribution of thermal infrared radiation emitted from Martian surfaces. The TES technique, can tell us much about the geology and atmosphere of Mars.

One can learn much about this method and the device by visiting the Arizona State University website pages that provide much more detail and background and reading through the TES News Archives.

[NOTE: The above curves actually exist on the Arizona State University website on their webpage address:]

Quartz, Feldspar & Hornblende Spectral Emissivies

The Thermal Emission Spectrometer is a scientific instrument and also Thermal Emission Spectroscopy is a measurement technique.

* K-feldspar end member KAlSi3O8, Albite end member NaAlSi3O8 or Anorthite end member CaAl2Si2O according to the Wikipedia article on Feldspar.
** The general formula (for Hornblende) can be given as (Ca,Na)2-3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2 , according to the Wikipedia article on Hornblende..