Type I belite grains are those that have crystallized from the liquid at
temperatures above about 1420•‹C and thus as a-C2S. The primary striations
arise on cooling through the u to u', 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',-
C2S that occurs on further cooling does not further increase the number of
orientations, but that from u', 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.