J. B. Scrivenor — Kaolin Veins, Federated Malay States. 81 



originally chiefly felspar, which has been altered to kaolin by 

 deep-seated changes during the last stages of the cooling of the 

 granitic magma. If that is incorrect, then the kaolin must have 

 been kaolin from the moment it consolidated, or it must have been 

 formed in recent times by weathering. With regard to this question 

 of the origin of kaolin, there is a marked difference of opinion 

 between British and American geologists. It is difficult to get one 

 of the former who has not visited the Tropics to allow that kaolin 

 can be formed by weathering at all. On the other hand, Lindgren, 

 in his Mineral Btposits, p. 305, writes as follows: "The idea 

 that the mineral may form by pneumatolysis, or the action of water 

 or gases liberated at high temperature from igneous magmas, is 

 assuredly untenable ; a strongly hydrous mineral, parting with its 

 water at the comparatively low temperatures of 300 to 400° C, could 

 not possibly originate in the presence of such minerals as topaz and 

 tourmaline." Lindgren favours an opinion that certain china-clay 

 deposits in Cornwall, generally regarded as of pneuraatolytic origin, 

 were formed by the weathering of sericitic granite, the sericite being 

 due to previous alteration by thermal waters. It is not necessary, 

 however, to postulate that kaolin was formed at the same time as 

 topaz and tourmaline. It may have been formed afterwards when 

 the temperature was lower; and, as kaolin formed by weathering 

 from the granite in the Malay States contains much of recognizable 

 felspar, unattacked or only partially attacked, the purity of the 

 Gopeng and other kaolin veins might be cited as pointing to a 

 different mode of origin. The objections to its having been kaolin 

 from the beginning are the same as those brought forward by 

 Lindgren to pneumatolysis, and even stronger when applied to this 

 idea and more applicable. Moreover, there is some, although not 

 good, evidence of felspar being present in small quantities. On 

 the other hand, if the kaolin is due to pneumatolytic action, why 

 do the large veins stop when the limestone is reached ? The 

 granitic vein on Kramat Pulai points to pneumatolysis, if it took 

 place at all, having been confined to rocks above the limestone, 

 and makes weathering seem less impossible as a mode of origin 

 than I once thought. It is to be hoj)ed that future excavations 

 on the tin-mines will give some decisive information one way or 

 the other. 



Specimens of kaolinite formed by weathering from felspar in 

 the Main Range granite at the Gap, Pahang, and specimens of 

 kaolinite from Gopeng and Kerling, have been compared with 

 kaolinite from a kaolinized felspar crystal in the Dartmoor granite. 

 The refractive index is about the same in all cases. The double 

 refraction is more marked in the Gap kaolin than in the others. 

 In the Gopeng specimen fan-shaped and vermicular aggregates of 

 plates are common. Vermicular aggregates also occur in the 

 Kerling specimen. The Gap kaolinite forms some aggregates of 

 parallel plates, and the kaolinite from the Dartmoor specimen 

 forms irregular flakes only. 



At the same time specimens of "Lenzinite" and " Glagerite ", 

 allied hydrous silicates of alumina, were examined. The Lenzinite 



DECADE VI. — VOL. V. — NO. II. 6 



