SCHALLER AND BAILEY: INTUMESCENT KAOLINITE 67 



MINERALOGY. — Intumescent kaolinite. W. T. Schaller and 

 R. K. Bailey, Geological Survey. 1 



A sample of kaolinite from eastern Oklahoma was sent in to 

 the Geological Survey for identification by Dr. C. N. Gould of 

 Oklahoma City. According to Dr. Gould, the mineral was re- 

 ceived by him from Mr. Tom Wall of Poteau, Oklahoma, who 

 stated that it forms vertical white streaks, one of which appears 

 to be about 20 inches thick, on Back Bone Mountain, about two 

 miles north of Williams, Le Flore County, Oklahoma. The de- 

 posit lies near the boundary of sections 2 and 3, T. 8 N., R. 26 

 E., Le Flore County. The mineral formed small compact lumps 

 with a glistening or fine satiny appearance. Examined micro- 

 scopically, the material was seen to be pure, homogeneous, and 

 well crystallized in minute hexagonal plates and crystals which 

 had all the appearance of kaolinite. The crystals average about 

 the following dimensions: c axis = 0.02 mm., b axis = 0.04 mm., 

 a axis = 0.06 mm. In testing the fusibility of the mineral it 

 was found to intumesce strongly and as no reference to any in- 

 tumescent kaolinite was found in the literature the material was 

 examined further for definite identification. It was found to 

 differ from kaolinite only in its intumescence. 



The crystals are too small and the birefringence too low for re- 

 liable results as to extinction angles and interference figures. 

 The refractive indices were readily determined and are as 

 follows : 



a(approx. parallel to c axis) = 1.561 

 /3(approx. parallel to a axis) = 1.563 

 7 (parallel to b axis) = 1.567 



Birefringence (7 — a) = . 006 



These values are close to those given for kaolinite. Kaiser 2 

 gives the refractive index as between 1.551 and 1.559, with a 

 birefringence of 0.005-0.006. His values for the refractive in- 

 dices are slightly lower than those here given. A possible ex- 



1 Published with the permission of the Director of the U. S. Geological Survey. 



2 Kaiser, Erich, tJber Verwitterungserscheinungen an Bausteinen I. Neues 

 Jahrb. f. Min. Geol. Pal., 1907: Band 2, 42-64. 



