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FrELD Columbian Museum — Geology, Vol. III. 



RUTILE 

 JEQUITINHONHA RIVER, BRAZIL 



FIG. I. PLATE LI 



Several crystals of rutile of an interesting habit were presented to 

 one of the authors by Olaf E. Ray, Esq., of the Chicago Brazilian 

 Diamond Company. The crystals were obtained by Mr. Ray from 

 sands washed for diamonds on the Jequitinhonha River near Diam- 

 antina, Brazil. The crystals are twins ranging from 9 mm. to 13 

 mm. in length and 8 to- 10 mm. in width in the direction of one 

 lateral axis while in the direction of the other lateral axis their thick- 

 ness is only 2 to 3 mm. The crystals have the typical brownish- 

 black color of rutile and are practically opaque but occasionally are 

 dark-red by transmitted light. The planes are splendent. Exami- 

 nation by the reflecting goniometer shows the crystals to be 

 made up of the ditetragonal prism h (210) and the pyramid of 

 the second order e (101). The development of the planes of the 

 pyramid is not uniform, two planes always being larger than 

 the other two. The twinning plane is v (301). The prismatic planes 

 are frequently striated parallel to the prismatic edges and hence 



