Palache — Notes on Tellurides from Colorado. 423 



apart from others. Through the kindness of Professor Hobbs 

 the writer was entrusted with two of the five type crystals of 

 the new mineral for examination and thus familiar with its 

 appearance, recognized it again in a specimen in the Harvard 

 collection secured some time before from Cripple Creek and 

 labelled as from the Little May Mine. Several measurable crys- 

 tals were obtained from the latter specimen and they were found 

 to agree in general with the two type crystals of goldschmidt- 

 ite examined. The author's measurements of Hobbs' two 

 type crystals confirmed in general his results as shown by the 

 table of angles given below but the use of the two-circle 

 goniometer made possible the measurement of a number of 

 minute pyramid planes which Hobbs had been compelled to 

 leave undetermined. These same forms and some additional 

 ones were also found on the new material, thus confirming the 

 identity of the two specimens. These pyramid forms, pro- 

 jected on the goldschmidtite axes, gave symbols far from 

 simple, and unsatisfactory relations with the other forms. 

 They were studied in gnomonic projection, and a comparison 

 of such a projection of the goldschmidtite forms on the clino- 

 pinacoid with a similar projection of sylvanite forms showed 

 a striking analogy between the two. By making the ortho- 

 pinacoid 100 of goldschmidtite equivalent to the orthodome 

 101 of sylvanite many forms of the first become identical with 

 known forms of the second, and the remainder, while appar- 

 ently new to sylvanite, receive comparatively simple symbols 

 on the sylvanite axes. In the following table the agreement 

 of angles of the common forms in the two principal zones is 

 well shown. 



Symbols 



Symbol 



Obs. 



Obs. 



Calc. 



Goldschm. 



Sylvanite. 



(Hobbs). 



(Palache). 



(Sylvanite). 



100 



110 



= 101 . 



121 



61°41' 



61° 41' 



61° 35£' 



100 



210 



= 101 



111 



42 43 



42 56 



42 45 



100 : 



230 



= 101 . 



131 







70 11 



70 10 



100 



310 



= 101 



323 



31 55 



31 40 



31 38£ 



100 



101 



= 101 



100 



55 35 



55 15 



55 08^ 



100 



: 201 



= 101 



001 



34 13 



34 16 



34 27 



101 



: 201 



= 100 



: ooi 



89 48 



89 31 



89 35 



100 



! 001 



= 101 



: 201 



89 25 



88 38 



88 48 



100 



: loi 



= 101 



: 201 



19 18 



19 30 



19 20 



Much had been learned concerning the crystallographic 

 character of goldschmidtite when the sylvanite crystals above 

 described came to hand, and their study helped to clear up 

 and make certain the relation between the two minerals. The 

 general similarity between the habit and forms of the two 

 series of crystals led to a surmise that a concealed twinning 



Am. Jour. Sci. — Fourth Series, Vol. X, No. 60.— December, 1900. 



28 



