﻿THE OCCURRENCE, COMPOSITION AND RADIOACTIVITY 

 OF THE CLAYS FROM LUZON, PHILIPPINE ISLANDS. 



By AxviN J. Cox. 

 {From the Chemical Dimsion, Bureau of Science, Manila, P. I.) 



INTRODUCTION. 



It seems hardly necessary to define a material of such common occur- 

 rence as claj r , still at the outset a good definition may more clearly indicate 

 some of its characteristics. Ries 1 says : 



The term clay is applied to a natural substance or rock which, when finely 

 ground and mixed with water, forms a pasty, moldable mass that preserves its 

 shape when air-dried and when burned, changes to a hard, rock-like substance by 

 the coalescence of its particles through softening under the action of heat. 



In other words, heat expels the volatile constituents, decomposes many 

 of the finely ground particles and causes the clay to sinter together. 

 Clays under the microscope are shown to be heterogeneous aggregates of 

 Irydrous and anhydrous aluminium silicates mixed with a variable quantity 

 of other crystals, mineral particles and impurities in all stages of decay. 

 The fact that silicate of aluminium is so characteristic a constituent 

 of clay is caused by this substance being one of the most insoluble of 

 natural compounds. The size of tbe crystals or particles varies from 

 0.01 millimeter up to grains distinctly visible to the naked eye. The 

 varieties of clays are extremely numerous, as they form a continuous 

 series ranging from pure kaolin (kaolinite) down to the more imperfect 

 varieties. This variance is caused by the increasing admixture with 

 kaolin of the common clays, consisting of other silicates of aluminium, 

 the silicates, oxides, carbonates, etc., of iron, calcium, magnesium, and 

 the alkalies, as well as free silica, and often organic matter. Kaolinite 

 itself may only enter into this mixture in a small proportion. This 

 variation is not surprising when we consider the difference in the compo- 

 sition of the original rocks from which the clays are derived. Kaolinite 

 (pure kaolin) is derived from the aluminous minerals, especially feld- 

 spar. 2 In practice it rarely exists in the pure state, since decomposition 



•P. S. O. S.,P.P. (1903), 11, 15. 



2 Dana, J. D. : A System of Mineralogy, New York (1900), 319, gives 23 

 analyses of this species from varied sources. The average is as follows ( figures 

 give percentages) : Si0 2 , 65.06; A1 2 3 , 19.27; CaO, 0.68; K 2 0, 10.85; Na 2 0, 3.68; 

 FeA, 0.16; MgO, 0.07; BaO, 0.05; ignition, 0.08; total, 99.9. 



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