W. E. Hidden — Edisonite, a new mineral. 



273 



those following e\ and of the angle m^m always varying some- 

 what from 90° I incline to believe that we have to do with a 

 dimorphous form of rutile I have adopted the sym- 

 bols a\ and e\ because in rutile the form a\ (=3 of Dana) is 

 unknown and it would give with the base an angle of 139° 48'. 

 It has always been said that dimorphous bodies have very 

 closely related crystalline forms and we have here an example 

 of a very near approach between the two forms. On the frag- 

 ments you have sent me I notice that the faces a\ and e\ differ 

 , in color and brilliancy. I trust you will succeed in procuring 

 some new specimens of dimorphous rutile."* 



I add to my own figures (1 and 2) and approximate angles, 

 the figure (3) given by DesCloizeaux and the angles observed 

 and calculated by him. The axial ratio given by him is 



& : b : c = 0-99275 : 1 : 0-92337. 

 The only natural faces observed are / and (fig. 1), the others 

 are cleavage planes. 



1. 2. 3. 



Hand goniometer, Hidden. Reflecting- goniometer, DesCloizeaux. 



Calculated. 



Observed. 



I *F = 140° approx. = al^a% = 140° 34' 140° 34' 



B~B' 



136 



I ~m 



133 



m ^ m"' 



90 



m ^mf 



90 



B „ra 



130 



I'~l" 



40 



el ^e£ 

 a\ ^m 



m /s ra 

 m *m 

 e\ *m 

 ok* ai- 



140° 18'. 



140° 24' 



131° 55'__ 131° 49' 



90° 25' 90° 25' 



89° 35' 89° 32-3' 



131° 30' 131° 42' 



38° 52' . 



39° 26' 



al = I, el = B, m = m, Faces of cleavage. 



Since Damour found only Ti0 2 , and this, if correct, would 

 prove it to be a fourth form of this acid, I questioned the 

 result because of its seeming improbability. A few careful 

 tests made by Mr. Mackintosh have confirmed the conclusions 

 of Damour. Recently Mr. S. L. Penfield has kindly under- 

 taken a complete analysis of the mineral, and I am happy to 

 be able to add his statement of the very satisfactory results 

 obtained. Mr. Penfield says : 



" The specific gravity, taken w T ith great care on 0*155 grams 

 of the mineral, was 4*285. Owing to the scarcity of material 



* A notice giving the above results was published by Professor DesCloizeaux 

 at the time. Bull. Soc. Mill., vol. ix, No. 5. 



