Lamellar textures in clinker belites

Type I belite grains are those that have crystallized from the liquid at temperatures above about I420°C and thus as a-C2S. The primary striations arise on cooling through the a to a transition, in which the symmetry decreases from hexagonal to orthorhombic, each set of striations thus representing a different orientation of the a structure. The transition to a -CjS that occurs on further cooling does not further increase the number of orientations, but that from o l to P, in which the symmetry falls to monoclinic, causes each orientation to split into two. This is the cause of the secondary sets of striations described above. 

Belite crystals have been observed that show only one set of striations. whose behaviour in transmitted light between crossed polars shows them to be twin lamellae. Such crystals are typically irregular in shape they have been called Type II belites, and are rare in modern clinkers. The striations arise from the aY to p transformation. Such crystals can form either by 

---