Abstract
Clinoenstatite from Papua was found to transform itself into a high-clino phase between 1, 050° and 1, 100°C. From its hOl precession photograph, a reasonable model of the structure was derived. Its probable space group is C2/c and lattice constants, a=9.93Å, b=8.79Å, c=5.34Å and β=110°15′. The SiO3-chain in the structure is very similar in the projected configuration but reverse in the way of puckering to the chain (A) in clinoenstatite. Neglecting the slight difference in the shapes of SiO3-chains, we can look upon the structures of high-clino and proto as built up of common unit slabs, whose arrangement according to gliding en echelon leads to the high-clino structure, and according to alternate gliding to the proto structure. The mechanism of transformations between the polymorphs of enstatite was also discussed in the light of the newly determined structure of high clinoenstatite.
