ON KAOLINITE FROM THE HAWKESBURY SANDSTONE. 175 



shaped crystals, and beside these, small hexagonal scales or fibrous 

 looking aggregates of micaceous minerals. 



The inference to be derived from the foregoing, is that under 



favourable conditions Kaolinite is first formed and that the rhombic 



.crystals (which may be exceedingly minute) by the three cleavages 



fbreak up into an extreme state of division, by mechanical action, 



.carbon dioxide, or other agency not yet determined.' We do not 



-jfind a different compound when formed into clay (kaolin) than 



what it is when crystallized Kaolinite ; it is hydrous silicate of 



...alumina when in crystals sufficiently large to be seen, and it is 



jhydrous silicate of alumina when these crystals are thoroughly 



.broken up.s tfeere is no chemical replacement of any of the elements 



when formed into clay (kaolin), and if it was not for impurities 



jthe composition of kaolin when in the finest state of division would 



not differ from that of Kaolinite when perfectly crystallized. 



Johnson and Blake state " that it is possible also that the 

 plasticity of clay is related to the form of the plates of Kaolinite, 

 perhaps to their thickness, but this is a subject that requires 

 further investigation." 



Did this mineral cleave only in one direction (the basal cleavage) 



the plates most probably would remain as such, and be as persistent 



as mica ; the composition of the product undergoes no alteration 



.as in the formation of serpentine ; and as the composition remains 



constant no matter how fine the division, it is evident that no 



. alteration from Kaolinite has taken place. 



To see how far this theory is likely to be correct, I took some 



. of the crystals, moistened them with a drop or two of turpentine, 



and ground them in a mortar, then transferred the paste direct to 



the slide. T found that nearly the whole of the larger crystals 



had disappeared, and that but a few isolated plates remained and 



these nearly all showing pieces broken from their edges along the 



. cleavages that break up these plates. Had the mechanical action 



of the grinding been continued a short time longer I am convinced 



that the whole crystallized appearance would have disappeared, 



. and that the exact resemblance of the clay from the deposits 



