52 



On the Homceomorphisrn of Mineral /Species 





Jersey chondrocyte is 68°. The great difference of angle for 

 these varieties of a single species should be considered, when 

 judging upon the differences among the several species in the 

 table. Taking 17 above as the unit dome, the vertical axis is 

 twice that given in the table, or 1.48352. In Chrysolite, also, 

 we have as good reason for doubling the vertical axis, in which 

 case it becomes 1.2584. In Caledonite, the occurring brachy- 

 dome has the angle 70° 57', and taking this as a unit dome, 

 axis a = 1.53136. 



The relations of Polianite to Gothite and Diaspore appear to 

 sustain the conclusion of Volger, cited in the American Journal 

 of Science, vol. xvii., p. 213. 



Euchroite is generally placed in a different position, and the 

 prism 117° 20' (form 17) is made the fundamental vertical prism. 

 But it forms no stellate or hexagonal twins like species of that 

 angle, and nothing appears to sustain that view in preference to 

 the one above taken. 



Bournonite has the same relation to the species of section II. 

 that Antimony Glance has to those of section I. It has very 

 nearly the angles of Topaz. 



Wohlerite has quite recently been studied by the able crystal- 

 lographer of Paris, M. Descloizeaux.* He gives for the verti- 

 cal prism, the angle 108° 56'. But 

 by comparing the range of angles 

 with those of the above species, it 

 appears that its true relations are 

 exhibited by the position in the an- 

 nexed figure, which is altered from 

 Descloizeaux. This gives for the 

 vertical prism, the angle 90° 54', 

 and for the unit domes, the angles 

 108° 2' and 108° 56', very near Andalusite. It appears to be 

 generally true that when a species affords for the prisms of two 



* Ann. de Chim. et de Phys., vol. xl., 3d series. 



