C. H. Warren — Miner alogical Notes. 371 



cible. The water was weighed directly by the method of 

 Penfield.* 



The results of the analysis are as follows : 



SiO Q _ 40-16$ 



A1 2 3 ... 34-89 



CaO_._ _ 18-26 



Na a O trace 



CaC0 3 5-30 



HO _ 1-69 





Mol. ratio. 





60 



= '669 



2-00 



02 



= '342 



1-02 



56 



= '326 



•97 



Graphite -18 



100-48 



The ratio of SiO a : AJ a 8 : CaO is nearly 2:1:1 as required 

 by the formula of anorthite, CaAl 2 (Si0 4 ) 3 . 



Feldspar Crystals, from Raven Hill, Cripple Creek, Colorado. 



The feldspar crystals were collected by Dr. Whitman Cross 

 of Washington, D. C, while engaged in making the geolog- 

 ical survey of the Cripple Creek region. They occur in con- 

 siderable numbers imbedded in a rather soft, light gray rock, 

 apparently of phonolytic character, the exact nature of which 

 is unknown, no petrographical study of the rock having thus 

 far been made. It is light gray in color, much altered in 

 appearance and occurs, as we are informed by Dr. Cross, as a 

 narrow dike cutting through the andesitic breccia of Raven 

 Hill, Prospect Shaft, on the eastern slope above the Moose 

 Mine. 



The feldspar crystals, which vary in size from individuals 

 5 mm in length and 3 mm in diameter' to those 15 mm in length, 

 10 mm in width and 8 mm in thickness, are of a light gray color 

 like their matrix, and have undergone some alteration on their 

 surface. The habit of the crystal is unusual in that the form 

 y, 201, is very prominent, while other forms b, 010 ; c, 001, 

 and m, 110, are relatively small, fig. 3. Twinning after the 

 Carlsbad law is common and gives rise to an appearance repre- 

 sented by fig. 4. In a large number of instances the crystals 

 form peculiar aggregates, sometimes several crystals penetrat- 

 ing through each other. No simple twinning relations other 

 than according to the Carlsbad Jaw could be discovered. 



The forms observed were: c, 001, o, 010, m, 110, and 

 y, 201, and below are the augles measured with a contact goni- 

 ometer, also the calculated values. 



*Ttiis Journal, xlviii, July, 1894. 



