Why Granular Media Are, After All, Thermal
  Granular media are considered "athermal", because the grains are too large to display Brownian type thermal fluctuations. Yet being macroscopic, every grain undergoes thermal expansion, possesses a temperature that may be measured with a thermometer, and consists of many, many internal degrees of freedom that in their sum do affect granular dynamics. Therefore, including them in a comprehensive approach to account for granular behavior entails crucial advantages. The pros and cons of thermal versus athermal descriptions are considered. 
Yimin Jiang and Mario Liu
cond-mat.soft