198 Penfield and Howe — Chemical Composition 



Humite, ( Type I of Scacchi.) 



In the course of the investigation we have been able to 

 examine only the humite from Mte. Somma, of which two 

 separate samples were analyzed. The material for the first of 

 these was obtained from a specimen purchased from Dr. A. E. 

 Foote of Philadelphia. The humite crystals, which measure 

 from 2-3 mm in diameter, are nearly colorless and transparent 

 and are associated with spinel and calcite. Their habit corre- 

 sponds in general to the figure of vom Rath* copied into the 

 sixth edition of Dana's Mineralogy, page 535. Some of the 

 measured angles are as follows : 



Measured. Calculated. 

 c^e 2 , 001 /, 104 =45° 29'' 45° 32£' 

 C/-.e 4 , 001^ 102 = 63 51 63 52 



c~e 6 , 001 A 101 — 76 17 76 13 



c^t-j, 001 ^ 1-2-10 = 44 9£ 44 8£ 



Measured. Calculated. 

 r 2 , 001 ^128 = 50°3H' 50° 30' 

 .rs, 001 ~ 126 = 58 16" 58 16 

 .is, 001^013 =55 45 55 44 



. * 3 ; 001 aOH = 76 59 77 12 



The material that was separated for analysis varied in specific 

 gravity from 3-194 to 3-201 



The material for the second analysis was selected from a 

 specimen in the Yale College cabinet, Catalogue No. 4102. 

 The crystals are associated with calcite and biotite. They are 

 chestnut brown in color, in habit like the ones described above 

 and were identified by the following measurements. 



Measured. Calculated. 



Ca« 2 , 001/^013 = 55° 44' 55° 44' 



C/s« 2 , 001^013 = 55 49 " " 



The specific gravity of the material for analysis varied from 

 3-183 to 3-225. 









First Analysis 









I. 



II. 



III. 



IV. 



Average. 



Ratio. 



Si0 2 



36-59 



36-63 



36-63 



36-68 



36-63 



•6105 



MgO 



56-34 



56-43 



56-59 



56-45 



56-45 



1-411 \ 

 •033 j 



FeO 



2-33 



2-43 



2-46 



2-30 



2-35 



F 



3-12 



3-06 



2-96 







3-08 



•162 ) 



H 2 



2-42 



2-48 







2-45 -=-9 



= -261 j 





100-96 









Oxygen 



equivalen 



t to F 



1-26 







99-70 









* Pogg. . 



inn. Erg. B. 



, v, Table VII, fig. 1. 





1-444 



•423 



