Synthetic enstatite MgSiO3 was crystallized from a melt, quenched into water, and then annealed at 873 K. The product is the monoclinic polymorph with
the unit cell parameters of a=0.9619(7), b=0.8832(3), c=0.5177(4) nm, β=108.27(5)°. Heat capacity was measured from 6 to 305 K using an adiabatic vacuum calorimeter. Thermodynamic
functions for clinoenstatite differ by about 5% from those predicted after a thermodynamic model in the literature, but are
very close to those measured for orthorhombic enstatite.