Twinning alite

Different 38 phases, in the case of low content of belite in clinker, is most convenient to identify using light microscopy. Among others, Metzger [161] applying this method found the presence of phase a. The striations of belite crystals always observed in industrial ehnkers due to polysynthetic twinning, are distinctly differentiate this phase from alite crystals and are formed in the polymorphic transformation process. 

The medium-temperature polymorph is monoclinic and biaxial negative X is parallel to c (trigonal), y is parallel to a (trigonal), and Z is perpendicular to a (trigonal), with the latter two relationships less firmly established. The 2 Vis 20° to 60°. In horizontal sections, alite may show irregular patches of threefold cyclic twins formed in the trigonal to monoclinic inversion uniform extinction occurs in vertical sections. 

A different interpretation of alite has been given by Fundal (1982), who stated that alite crystals are twinned individuals of a lower symmetry which imitate a higher symmetry (a mimetic relationship). The monoclinic form of alite was said to have an index of refraction of 1.72 and a birefringence of approximately 0.0050. Tri clinic alite was reported to be polysynthetically twinned in a fused clinker and have a birefringence of 0.0020. Alite birefringence, however, exhibits two average val ues in Fundal s Table 1 (1982) 0.0043 (monoclinic) and... 

Polysynthetic twinning (very minute) in alite Triclinic alite due to failure to absorb enough impurities at high temperatures (Ono, 1975)... 

Alite with spindle or lancelike bands Monoclinic to triclinic inversion (Gille and others, 1965) twinning (Maki, Haba, and Takahashi, 1983)... 

Photograph 7-27 Ragged belite crystals and belite coating on alite, one of which is twinned. Note abundant dotlike impurities in alite. Coarsely crystalline matrix with gray aluminate and relatively bright ferrite. Slowly cooled clinker. (S A6647)... 

Photograph 7-75 Brown prismatic (alkali-rich) aluminate crystals, some entrapping alite and appearing zoned or twinned along a prism face. Dry-process kiln. (S A6693)... 

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