The equilibrated grain boundary groove shapes for commercial purity pyrene (PY) were directly observed by using a temperature gradient stage. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient and solid-liquid interfacial energy of PY have been determined to be (8.9 +/- 0.9)x10(-8) K m and (21.9 +/- 3.3)x10(-3) J m(-2) with the present numerical model and Gibbs-Thomson equation, respectively. The grain boundary energy of PY phase has been determined to be (42.8 +/- 7.3)x10(-3) J m(-2) from the observed grain boundary groove shapes. Thermal conductivity ratio of liquid phase to solid phase has also been measured to be 0.89. (c) 2006 American Institute of Physics.