Examination of the Diopside of Fassa in the Tyrol. 351 



I. Mineralogical and Chemical Examination of the Diopside of 

 the Valley of Fassa. 

 This diopside, in the state I received it, consisted of single 

 loose crystals, which appeared to have been attached. They 

 usually are a couple of inches long, and are mostly compressed, 

 so as to appear flat. They are generally free from extraneous 

 substances, and I saw only a few crystals covered on their 

 surface with laminae of chlorite. But they are found more 

 frequently covered with a gray tarnish or bloom resembling 

 iron, which is especially perceptible near the ends, and seems 

 to have at times come out from the mineral itself, in which 

 case it also seems more intimately connected with it. 



I am indebted to the obliging kindness of my respected 

 teacher Counsellor Hausmann, for the following crystallo- 

 graphical communication on the diopside of the valley of 

 Fassa. 



" The crystals of diopside, usually broken at the ends, pre- 

 sent themselves most frequently as rectangular prisms, the 

 greater sides of which are more or less striated longitudinally, 

 whilst the other sides are either smooth or slightly striated. 



" The appearance of planes replacing the lateral edges ex- 

 plains the nature of the surface of these rectangular prisms. 

 For the planes agreeing with the planes E of the prism of au- 

 gite, which, according to Haiiy, are respectively inclined at 

 92° 18' and 87° 42', the narrower planes of the sides which 

 form with the replacing planes an angle of 136° 9', present 

 themselves as the planes B', and the broad ones as the planes B. 

 " Sometimes the planes BB' 3 (f) appear perfectly formed, 

 making with each other angles of 141° 44?' and 38° 16'. A 

 disposition to the formation of these planes is distinctly dis- 

 covered in the deep striation of the planes B. 

 " The observed combinations are : 



2 B'. 2 B 



2 B'. 2 B. 4 E. 



2B'. 4BB'3. 



2 B'. 2 B. 4 BB'3 



2 B\ 4 E. 4 BB'3. 

 " The respective inclinations of these planes are, the angles 

 given by Haiiy being taken as the basis, 



B' - B = 90° 0' 



B' - E = 186 9 



B - E = 133 51 



B' - /= 109 8 



B - /= 160 52 



E - /= 152 59 



/ - / = 141 44 



Sometimes 



