818 Weed and Pirsson — Missourite, a new Leucite 



As the presence of actual leucite itself has never before been 

 demonstrated, so far as we know, in a granular plutonic rock, 

 it became a matter of importance to prove its identification 

 beyond all doubt. 



For this purpose a considerable portion of the rock was 

 crushed, sifted, washed, and treated with the potassium mer- 

 curic iodide solution. Immediately all of the ferro-magnesian 

 minerals sank, leaving the white component floating. On then 

 lowering the specific gravity by dilution, nothing except an 

 occasional grain fell until 2465 was reached, when a very little 

 of the white powder came down. This under the microscope 

 proved to consist of isotropic grains with attached particles of 

 pyroxene and biotite which had evidently increased their spe- 

 cific gravity. This behavior of the rock powder in the heavy 

 solution proves the absence of all feldspars and nephelite, thus 

 confirming the microscopic examination. On now lowering 

 the specific gravity of the liquid to 2405, the great bulk of the 

 white component came down, leaving a small portion floating. 

 The average specific gravity of this material may be taken as 

 244:. Examined under the microscope it was found to be a 

 very pure product, consisting of clear isotropic grains which 

 here and there showed a faint birefraction. An analysis of it 

 (by L. y. Firsson) gave the following results : 



SiO, 5446 



Al.Og 22-24 



Fe^O^ -68 



MojO trace 



CaO -10 



K^O 18-86 



Na^ -70 



HO _._ 2-29 





Molecular ratios. 



•907 



•90V = 4^12 = 4 



•216 ) 

 •004 



•220 = 1 = 1 



•002 

 •200 ( 



•213= -97 = 1 



•Oil J 





99^33 



The formula is therefore KAl(Si03)2 and the mineral is 

 consequently leucite. There appears to be a very slight defi- 

 ciency of alkalies, and this may be due in part to replacement 

 by water, whose presence is undoubtedly due to processes of 

 zeolitization which are commencing and which may be in part 

 the cause of the faint birefraction noticed above. The small 

 amount of soda shows the leucite to be a very pure potash 

 compound. So far as we know, this is the first analysis of a 

 leucite from other than an Italian locality, with the exception 

 of that given by Steinecke* of the mineral from Choi in 

 Persia. 



* Jiingere Eruptivgesteine aus Persien, Inaug. diss., Halle, 1887, p. 12. 



