W. T. Schaller — Natramblygonite, a New Mineral. 49 



cleavages intersecting at about 70°. In its general appearance 

 the mineral very much resembles massive amblygonite. The 

 hardness is 5*5 and the specific gravity lies between 3*01 and 

 3 - 06 with an average value of about 3-04. The luster is vitre- 

 ous inclining slightly to greasy. The color is greyish white 

 to white. In the hand specimen, it is translucent to opaque. 



Examined in thin section under the microscope, inclusions 

 of quartz, feldspar and mica were seen and also an irregular 

 distribution of a kaolin-like dust. Two directions of polysyn- 

 thetic twinning lamellae intersecting at about 86° are promi- 

 nent and lie at an angle against the cleavage cracks. The 

 best cleavage is nearly normal to a bisectrix, and the section 

 parallel to this cleavage shows a biaxial interference figure 

 with a large angle. Its sign is negative. 



Heated in a blowpipe name, the mineral easily fuses, with- 

 out decrepitation but with slight intumescence, to an opaque 

 white enamel. The flame is colored yellow with no indication 

 of red, due to lithium. In this particular, natramblygonite 

 differs markedly from amblygonite and can thereby be distin- 

 guished from the common mineral. It would be well to test 

 amblygonite from different localities by this flame test. 

 Heated in a closed tube, water is given off and the mineral 

 then quietly fuses without decrepitation to a blebby enamel 

 firmly fused onto the glass tube. 



Chemical composition. — Analysis of a selected sample of 

 natramblygonite gave the values shown below. The sample 

 was finely crushed and all visible impurities and doubtful look- 

 ing pieces picked out by hand under a magnifying glass. The 

 final sample all sank in Thoulet solution of density 3-01+ and 

 all floated in solution of density 3"06. Beryllium was tested 

 for but could not be detected. The mineral is difficultly solu- 

 ble in H 2 S0 4 , in which solution no calcium could be found. 



Analysis and ratios of natramblygonite. 



P.O.- — 



Al O ... 



44-35 



33-59 



•312 1-00 

 •329 106 



■"'as 



Li 8 0._„ 



NaO... 



3-21 



11-23 



•107 ) 



•181 V-289 -93 



K.O 



-14 



•001 ) 



H.O+ . 



4-78 



•266 -85 ) 



P 



5-63 



•296 -47F 2 [ 



Less O for F 



102-93 

 2-37 











Am. Jour. Sci.— 

 4 ' 



100-56 

 -Fourth Series, Vol. 



XXXI, No. 181.— January, 



1-32 



1911. 



