204 University of California Publications. [Geology 



directions for quartz, and his results bear out the conclusions 

 of Savart* that the elastic properties in various azimuths possess 

 the asymmetry characteristic of rhombohedral tetartohedral 

 crystallization. His results were computed from bending tests, 

 with the load applied in the middle, and E was the unknown 



p P 



quantity in the bending formula y = 4jE &rf a - 



The values of Ej expressed in grams per sq.mm. were : 



E = 10,304,000 parallel to c. 



E-45 = 13,050,000 perpendicular to — Li. 



#445 = 8,405,000 perpendicular to +B. 



#90 = 7,850,000 perpendicular to c. 



Fl Fl 

 For linear dilatation, E or Jf=-— or e= j|— . 



For thermal expansion, e = l (fa — ti) c. 

 Combining, F=Ma (t-i — ^i) c, which measures the force to be 

 applied to keep the body from expanding under the given con- 

 ditions. If we take a cubic foot of quartz in which the c axes 

 are all parallel, we shall have the force of expansion for a rise 

 of temperature from 0° to 100° C to he 

 10,304,000 



453.6 X 2000 

 and 

 7,850,000 



v'(12X25.4) 2 X .00078 = 820 Tons per sq. ft. parallel to c 

 X (12 X 25. 4) 2 X- 00141 = 1140 Tons per sq. ft. perpendicular to c. 



453.6 X 2000 



These results are remarkable, but not nearly as startling as 

 they might be. For here the modulus is large where the thermal 

 expansion is small, and the two tend to neutralize each other. 



A case that would come nearer to some of the schists studied 

 would be one in which mica or hornblende is the main mineral. 

 In many mica schists the micas all lie in the same plane, having 

 their c axes parallel, while in some hornblende rocks the horn- 

 blendes have all three axes roughly parallel. 



Gypsum has in the plane of its clinopinacoidal cleavage 

 moduli whose values vary from 3.lXl0' ; to 8.6X10°| ; but values 

 perpendicular to the cleavage have not been worked out because 



* Pogg. Ann. Btf. XVI, p. 206, 1826. 



t Taken from his remarkable paper in V. 5 of the Beiblatter des Jahr- 

 buches fur Cryst. Min. u. Paleont. 



t L. A. Coromilas. liber die Elasticitatsverhaltnisse in Gyps und Glim- 

 mer. Inaug. Dis. Tubingen. 1877. Eeviewed in Zeit. fur Kryst. V. I, p. 407. 



