20O NEW YORK STATE MUSEUM 



the disposal of the writer for study. The specimen consists of a 

 mass of titaniferous magnetite forming portion of a joint plane in 

 the ore body. The surface of the joint is covered with small 

 crystals of magnetite of cubic habit closely associated with werner- 

 ite in small transparent crystals. The comparative rarity of the 

 cubic crystal habit in connection with magnetite 1 together with the 

 adaptability of these crystals to measurement, has rendered advis- 

 able the following brief note : 



The magnetite crystals which average 2 millimeters in diameter 

 are exceptionally brilliant, well developed and free from distortion. 

 The simpler combination which is shown in figure 3 consists of the 

 cube a (100) developed to a dominant crystal habit and modified 



Fig. 4 Magnetite, Split Rock 



by the octahedron 0(111) and the dodecahedron d(no), both of 

 these latter forms being present in small development. A more 

 complex combination is shown in figure 4 and consists of the above 

 forms developed to about equal habit and modified by the trigonal 

 trisoctahedrons 01(331) and k(552) and by the new trapezohedron 

 W = jOj== (71 0- They He well in zone, the faces of the trigonal 

 trisoctahedrons and of the dodecahedron being markedly striated 

 parallel to the zone [100.110]. The planes of the trapezohedron 

 qr(jii) are small but extremely bright and give excellent reflec- 

 tions. The forms were identified from measurements obtained 

 from five of the best crystals. 



1 Magnetite crystals of cubic habit were noted by H. Sjogren from 

 Mossgrufva, Nordmark. Bui. Univ. Upsala. 1894-95. 2.63. 



