Belite clusters and crystal sizes  Belite crystals begin to form in a kiln feed at quite an early stage of burning at contact points between silica and lime particles.   Very fine, poorly formed crystals can be present at temperatures below 800 ᵒ C, before the feed has entered the rotary kiln in a preheater system. The mineral belite is normally present in the cement kiln as one or more of three polymorphs known with increasing formation temperature as β , α ’ (alpha prime) and α . There is also a lower temperature form γ which is very rare in clinker and also the α ’ is subdivided into low and high temperature forms.  In the cement kiln as the temperature rises above 1100 ᵒ C   belite is present as α ’ crystals. These are very fine, relatively pure crystals which grow only slowly until, at about 1400 ᵒ C, they undergo a transformation to larger crystals of α belite. The α form absorbs impurities as it rapidly grows. In the burning zone of the kiln most of the belite crystals