316 . H. Ries — A Peculiar Type of Clay. 



Art. XXYI. — A Peculiar Type of Clay ; by H. Eies. 



The clay referred to in this paper was received by the writer 

 from western Texas, and is of such unusnal character as to be 

 worthy of record. On superficial examination it appeared to 

 be a gritty clay resembling loess. When mixed up with water 

 it developed sufficient plasticity to permit its being molded 

 into bricklets without difficulty, and these when fired at 950° C. 

 baked to a porous body of moderately hard nature, but which 

 on exposure to moisture disintegrated completely, indicating 

 that the clay contained a high percentage of either lime or 

 magnesium carbonates. 



It was the microscopic examination of the material that 

 showed its extraordinary character, for it was found to consist 

 almost entirely of small rhombs (fig. 1) of varying size but 

 averaging about 'OOS""' in diameter. The quantity of very fine 

 undeterminable clay particles was practically negligible. A 

 chemical analysis showed the clay to contain 98^ per cent dolo- 

 mite and \\ per cent iron oxide and alumina. From the above 

 it is seen that the clay is made up almost entirely of dolomite 

 rhombs, and so far as the writer is aware is different from any 

 clay that has been described. 



While it may appear incorrect to some to call this material 

 a clay, it is nevertheless such in the physical sense, being 

 macroscopically an earthy material possessing distinct plasticity 

 when wet. Mineralogically and chemically it is far from a 

 normal clay in its composition. Most clays on chemical anal- 

 ysis show an appreciable percentage of alumina, which may 

 range from as little as 10 per cent (or even less in a few) in 

 many impure clays, up to 38 or even 40 per cent in high grade 

 fire clays and china clays. The clay here described is therefore 

 most abnormal in respect to its alumina content. 



There are of course a great many calcareous clays which may 

 contain a large amount of lime and magnesium carbonates, but 

 none of these approach the type under consideration. Thus in 

 a series of Wisconsin clays, the maximum percentage of carbo- 

 nates found in one was, 22*48 percent CaO, and 8"95 percent 

 MgO.* A more extreme case is represented by a clay from 

 Seguin, Guadeloupe County, Texas, which contained 41*30 

 per cent CaO, but only *42 per cent MgO.f None of these 

 clays therefore approach the present case in total carbonates, 

 and fall far below it in magnesium contents. 



The extraordinary difference does not end here, but applies 

 to the texture. Most clays when examined under the micro- 



*Ries, Wis. Geol. and Nat. Hist. Surv., Bull, xvi, p. 105. 



f Eies, Clays of Texas, Bull. Univ. Tex., No. 102, p. 200, 1908. 



