244 Dana and Penfield — Crystalline form of Polianite. 



Of the half dozen specimens in hand, one (A) was especially 

 suited for accurate crystallographic and chemical work (Y. TL, 

 2143). It exposed a crystalline surface consisting of closely 

 compacted composite individuals, and upon this were thickly 

 implanted numbers of small highly modified bead-like crystals 

 with more or less brilliant faces. The relation between these 

 small crystals and the mass of the specimen was not obvious at 

 once, but as soon as the former had been made out it was seen 

 that the composite crystals were identical with the others in 

 form, each one being made up of a multitude of individuals in 

 parallel position. Closer inspection showed also that the appar- 

 ently simple small crystals were also often composite. The 

 larger crystals were often rhombic in habit and were terminated 

 by a large basal surface formed of the vertices of the closely 

 compacted pyramids. The form of these crystals is shown in 

 figs. 1 and 2. 



The planes present are : 

 ft(210. i-2), e (101, l-i), 3(321, 3-f), and also the form m (110, 1) in traces. 



The planes of the prism h are rather rough and uneven ; those 

 of e are brilliant but uniformly rounded on either side of the 

 vertical diagonal, showing a tendency to develop into two 

 vicinal pyramidal planes ; the planes of the zirconoid z are 

 usually brilliant and give good reflections. Having before us 

 the description of Breithaupt and the apparently confirmatory 

 results of Kochlin, our attention was especially directed at first 

 to the question as to the system to which our crystals belonged 

 and their relation to Breithaupt's form. A large number of 

 measurements consequently were made, some of which are 

 given beyond, but while they showed considerable variation 

 among themselves, more than the character of the faces seemed 

 to justify, they did not conform to the orthorhombic form, 

 although approximating to the angles of Kochlin. 



A second specimen in hand (Y. TL, 2154) showed a mass 

 of quartzose rock, and in a cavity in it a considerable amount 



